MRF2800 Rectifiers Handbook and Application Notes

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Contents Chapter 1

Introduction

3

Chapter 2

Connectors and Pinouts

4

Chapter 3

Installation and Operating Instructions 3.1 Safety 3.2 Mounting and Ventilation 3.3 Connections 3.4 Front panel adjustments 3.5 Parallel operation 3.5.1 Without Forced Current Sharing 3.5.2 With Voltage Droop Current Sharing 3.5.3 With Forced Current Sharing 3.6 Voltage Control and Programming 3.7 Current Control 3.7.1 Current Monitor 3.7.2 Current Limit 3.8 Auxiliary Supply

6 6 6 6 6 7 7 7 7 8 9 9 9 10

Chapter 4

Signals 4.1 Signals Overview 4.1.1 Basic Signals 4.1.2 Extended Signals 4.1.3 Extended Signals + Float/Boost Control 4.2 Isolated Signals 4.2.1 Signals and LEDs 4.2.2 Signals Configuration

11 11 11 11 11 12 12 12

Chapter 5

Switch Settings

13

Chapter 6

Thermal Control 6.1 Thermal Control of Current Limit 6.2 Control of Fan Speed

14 14 15

Chapter 7

Safety and EMC 7.1 Safety 7.1.1 CE Mark 7.1.2 EN60950 / IEC950 7.1.3 Energy and Voltage Hazard Warnings 7.2 EMS

16 16 16 16 16 16

Chapter 8

Maintenance

17

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1. Introduction Overview The MRF2800 Rectifier range are a.c./d.c. converters specifically designed for high power battery charging applications in stand-by systems. All models have sine wave corrected input and most operate from 230V nominal 50/60Hz ac input. The MRF28H54BV50 operates from 277V nominal 50/60Hz AC input and provides a nominal output voltage of 54.5V. An output power of 2800W is available at a nominal voltage of 54.5V (max ambient 65C) or 27.25V (max ambient 55C). Cooling is provided by an internal, variable speed fan. MRF2800 have rear hot plug connectors suitable for blind mating the rectifier into a suitable shelf such as the APC MS28* family.

Product part numbers This handbook applies to the following products: Product

Output voltage

Maximum current

Signals

1MRF28H27A

27.25V

100A

Basic

1MRF28H27B

27.25V

100A

Extended

1MRF28H27D

27.25V

100A

Extended + current limit / OVP adjust

1MRF28H54A

54.5V

50A

Basic

1MRF28H54B

54.5V

50A

Extended

1MRF28H54BV50

54.5V

50A

Extended

1MRF28H54D

54.5V

50A

Extended + current limit / OVP adjust

One or more further characters can be appended to the above base part numbers : | V or H is used to denote the front panel style, Vertical units have a 4U high front panel, while Horizontal units have a 3U high front panel, with the rectifier body rotated through 90 degrees. | N is used to denote non-SELV units, with a higher 63V maximum output. | Digits 00 though 99 denote a specific configuration of the product, e.g. output voltage set to a nonstandard value Throughout this handbook product numbers containing one or more * characters refer to products in the above table where the * can represent any character valid for this table. For example, MRF28H54* can be any of MRF28H54A or MRF28H54B or MRF28H54D.

For the complete electrical and mechanical specification refer to the product data sheet.

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2 . Connectors and Pinout Connector types Customer / Backplane Mounted part Product Number 1MRF28H***

Function Mains input

Connector Type Positronic "Power Connection Systems" series

Style

Manufacturer & part number

APC part number

Straight

Positronic

721-0101

SK2791 90 deg

Positronic

770-0219

SK2887 1MRF28H*** 1MRF28H***

DC Output Signals

Tin plated brass bus bars, 25.4mm x 3.2mm DIN41612 type B 32way

Elcon Crown Clip

721-0100

538 17 001 00 (2 per) Straight

Siemens

725-0033

V42254-B2202-B320 90 deg

Siemens

725-0034

V42254-B2200-Q320 1MRF28H***

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Straight

1MKC2801

90 deg

1MKC2802

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Pinout Signals connector pin no.

Function MRF28H**A

MRF28H**B

MRF28H**D

Notes

a1

N/C

N/C

N/C

a2

N/C

Fan Fail

Fan Fail

a3

Post Mate Enable

Post Mate Enable

Post Mate Enable

a4

N/C

Standby opto

N/C

a5

N/C

Programme down

Programme down

Connect +5v with respect to optos common. Available current 100mA

Connect to - sense to run unit

a6

Floating +12V

Floating +12V

Floating +12V

a7

N/C

N/C

N/C

a8

N/C

Over temperature opto

Over temperature opto

a9

N/C

Thermal control opto

Thermal control opto

a10

Relay normally closed contact

Relay normally closed contact

Relay normally closed contact

a11

Relay common

Relay common

Relay common

a12

Relay normally open contact

Relay normally open contact

Relay normally open contact

a13

Current share

Current share

Current share

a14

N/C

Remote shutdown (com)

Remote shutdown (com)

a15

N/C

Remote shutdown (+ve)

Remote shutdown (+ve)

Connect +5v with respect to Remote shutdown (com)

a16

Marginate (down)

Marginate (down)

Marginate (down)

Connect to +sense.

b1

N/C

N/C

N/C

b2

N/C

Boost select.

Boost select.

b3

N/C

Boost indicate opto

Boost Active opto

b4

N/C

N/C

N/C

b5

N/C

N/C

N/C

b6

N/C

Current limit program

Current limit program

b7

N/C

I_out >15% opto

I_out >15% opto

b8

- sense

- sense

- sense

b9

V-trim port

V-trim port

V-trim port

b10

N/C

Over voltage opto

Over voltage opto

b11

N/C

Current limit opto

Current limit opto

b12

N/C

Output healthy opto

Output healthy opto

b13

N/C

Input healthy opto

Input healthy opto

b14

0V float

Optos com / 0V flt

Optos com / 0V flt

Optos common and 0V float

b15

Current monitor

Current monitor

Current monitor

0.1V per amp output

b16

+ sense

+ sense

+ sense

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Relay is energized when the rectifier output is healthy, i.e a11-a12 becomes short circuit, a10-a11 becomes open circuit

Connect +5v with respect to optos common.

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3. Installation and Operating Instructions 3.1 Safety and EMC The rectifier is intended to be accessible only to authorised personnel; user access should be prevented by mounting in a suitable enclosure. See chapter 7 for further information regarding safety approvals and EMC. WARNING Hazardous voltages exist at various points within the unit. Disconnect the mains supply and wait at least 3 minutes before removing any covers. If the unit requires servicing it is recommended that it be returned to the manufacturer at the address given. Any repairs attempted must be carried out by qualified personnel conversant with modern switch mode power supply technology.

3.2 Mounting and Ventilation All models are designed for mounting in rack systems with the internal fan providing cooling. Provision must be made for the free flow of cooling air into the front face of the rectifier, and free exit from the rear (connector) face. MRF2800 rectifiers are designed to thermally protect in situations where there is inadequate airflow; the protection mechanism is described in detail in chapter 6.

3.3 Connections Connectors are required for the rectifier as specified in chapter 2. MRF2800 rectifiers will not operate until pin a3 (post mate enable) is connected to pin b8, and a 1 second delay is included to allow the connector mating process to be completed when the unit is pushed into its rack before power is available from the output connectors. All versions of MRF2800 rectifiers include an output protection diode which will prevent current feedback into the unit when the output is connected to an external power bus.

3.4 Front panel adjustments Units with basic signals do not have any external adjustment potentiometers. Output voltage can be adjusted by the application of an external voltage trim port. (See below). Units with extended signals (see chapter 1) have two output voltage levels, Float and Boost. These two levels are set by independent front panel pots. Selection of float or boost voltage is done with either a front panel switch, OR a digital input signal (pin b2). The default condition is float. In addition, "D" version units have independently adjustable current limits for the float or boost condition, and a front panel adjustable overvoltage trip level.

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54V rectifiers Set to Set to boost float Output volts range Current limit range Overvoltage range Output volts factory default Current limit factory default Overvoltage factory default

52 - 58V 25 - 52A 58 - 63V 54.5V 51A 59.5V

53 - 60V 20 - 52A 58 - 63V 57.6V 40A 59.5V

27V rectifiers Set to Set to boost float 26.0 - 29.0V 26.5V - 30V 50 -102.5A 40 - 102.5A 29.0 - 31.5V 29.5 - 31.5V 27.25V 28.8V 102A 80A 31.5V 31.5V

3.5 Parallel Operation 3.5.1 Without Forced Current Sharing If the connections from the rectifier to the load are very short, then no load current sharing between the rectifiers will occur. The rectifier with the highest set output voltage will supply all the load current until it reaches its current limit point, when the rectifier with the next highest set output voltage will start to provide load current, until it reaches its current limit point; and so on. The rectifiers are able to operate under these conditions, but it may be desirable to distribute the load more evenly. Some load current sharing can be achieved by arranging the connections from the rectifiers to the load to be star-point connected at the load and allowing the output voltage to droop slightly via each load lead. Resistance as small as 3-4mΩ in the connections between the rectifiers and the star point will cause reasonable current sharing.

3.5.2 With Voltage Droop Current Share Passive current sharing can be improved by selecting the voltage droop current share mode. DIL switch number 4 (located on the side of the rectifier) enables this mode when on. The output characteristic of the rectifier simulates an output impedance of approximately 20mohm. Hence the output voltage will fall by 1V between off load and 50A. This helps counterbalance variations in load lead resistance between parallel rectifiers. The obvious downside is "poor" load regulation (27V units : 5mohm for 0.5V drop at 100A)

3.5.3 With Forced Current Sharing Accurate current sharing can be achieved without voltage droop and star point connections. Rectifiers can be forced to share the total load current by connecting their current share ports together.

Figure 3.1 shows the recommended methods of connection in forced current share.

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The forced current share port is referenced to the negative sense terminal and so imposed differences in potential between the negative sense terminals of the paralleled units will degrade the accuracy of the sharing. For local sensing, Figure 3.1A, it is therefore desirable to star-point the negative power connections to achieve the best load current sharing. The range of control of the forced current share port is limited to a +1% differential in the output voltage of paralleled rectifiers. Thus for systems using local sensing it is recommended that the positive power connections are star-pointed too, to limit the differentials between sensed output voltages. When using remote sensing, Figure 3.1B, the power connections can be made in any convenient manner, provided the respective positive and negative sense terminals of each rectifier are connected together and single sense connections made at the load. Rectifiers are supplied with the sensing set to local by default. This can be adjusted by altering the settings of the red DIL switches which are accessible from the outside of the unit, switch 1 controls the connection of +ve sense, switch 2 controls the connection of -ve sense. For switch access and setting see chapter 5. If circuit breakers are used in either the positive or negative power connections, then local sensing must be employed. This ensures that each rectifier can locally control its output when not connected to the rest of the system. While the connection methods of Figure 3.1 are the most desirable, the rectifier is tolerant to many variations of connection. While current sharing is not guaranteed if other methods are used, the rectifier will not be damaged and will not produce voltages above the overvoltage trip level.

3.6 Voltage Control and programming The group of connections +sense, marginate down, v-trim and -sense shown in figure 3.2 allows the user to accurately control the output voltage of the rectifier. The pins allocated to these connections are detailed in the appropriate table in chapter 2. It is intended that the rectifier can be operated with no connections made to these pins at all. In this condition DIL switches 1 and 2 internally connect the positive and negative sense terminals to the positive and negative output terminals respectively. This provides local voltage sensing and the voltage at the output terminals is regulated very accurately.

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If the voltage at the load terminals needs to be regulated accurately and the power lead resistance is large enough to cause poor regulation, then remote voltage sensing can be used as in figure 3.1B. To remove the internal local sensing set the red DIL switches 1 and 2 to OFF. Connections must then be made between the two sense pins and the point at which accurate regulation is required. A preset reduction in the output voltage of typically 2.5V can be achieved if marginate down is connected to +sense. An external control circuit can be used to vary the output voltage over a limited range. V-trim is connected to the voltage control circuit via a high impedance. The open circuit voltage at this point is preset to 5.1V (via 32kΩ) with respect to -sense; output voltage adjustment is achieved by sinking or sourcing current (1mA max.) through this port. As the voltage applied to v-trim is moved from +5.1V to +10V the output voltage will linearly reduce from 54.5V to 48V (27.25V to 24V for 27V product); moving the voltage applied to V-trim from +5.1V to +0V will cause the output to linearly increase from 54.5V (27.25V) to the OVP trip level. The V-trim lines of all units in a system may be linked for common control of all the rectifiers (the -sense lines must also be linked), but this connection must be driven by an external voltage source. If this is not done, then rectifier failure, hot-plugging and system power-up will cause significant deviations in output voltage. In complex power systems, the "Power Management System" will usually have an analogue output for adjusting system voltage, and this can be connected to the V-trim port. The circuit shown below can be used to drive the V-trim port on multiple rectifiers, with pot P1 allowing adjustment of all rectifiers simultaneously. It is recommended that one of these circuits to fitted to each rectifier shelf in a rack system. The power management system can still be connected via R9, and will override the local pot setting. A fixed offset down can be applied to the output voltage by setting red DIL switch 3 ON; this will reduce the output voltage by 5V (2.5V for 27V product). For DIL switch access and setting see chapter 5.

3.7 Current Control 3.7.1 Current monitor The current monitor output produces an analogue signal referenced to -sense that is proportional to the current being delivered by the rectifier; the gain is 0.1V/amp for both 54V and 27V rectifiers (i.e. 50A results in 5.0V). A suitable ammeter can be directly connected as the output impedance of the signal is 5.1kΩ.

3.7.2 Current limit Rectifiers are supplied with the current limit characteristic set by default to foldback; the current limit performance is illustrated in figure 3.3 below. Alternatively, the characteristic can be altered to constant current by setting red DIL switch 5 OFF

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The current limit program pin allows the user to reduce the current limit point of the rectifier. This is achieved by connecting a resistor between this pin and negative sense; the resultant current limit level is illustrated in figure 3.4 below. The current limit cannot be programmed higher than it is with this pin open circuit

3.8 Auxiliary supply A 12V 100mA auxiliary supply is provided which is floating with respect to the rectifier output, with its negative return line (0V float) connected to optos common This supply is protected against short circuit and excessive voltages connected in parallel. It can be used to power any external signal or control circuitry the user may wish to connect to the rectifier, and is present whenever AC input is connected to the rectifier regardless of the rectifier output status.

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4. Signals 4.1 Signals overview A comprehensive signals package is available for MRF2800 rectifiers. Basic signals are included with every version, whereas products with part number suffix B or D (see table in chapter 1) have signals cards fitted which provide extended signals.

4.1.1 Basic Signals Rectifiers with part number suffix A have the following basic signals: O/P healthy relay contacts (Green LED mimics o/p healthy contacts) Remote sense Voltage trim port Marginate down Current share port Analogue current signal

4.1.2 Extended Signals (B) Rectifiers with part number suffix B have the following extended signals in addition to the basic set described above. Digital outputs mimicked by front panel LEDs: Input healthy Output current Overvoltage Thermal control In standby Fan Fail Digital inputs: Inhibit / OVP reset

In current limit Over-temperature

Programme down

Digital inputs and outputs are isolated from the rectifier power output with optocouplers and are described in section 4.2 below.

4.1.3 Extended signals (D) Rectifiers with part number suffix D have the following extended signals in addition to the basic set described above. Digital outputs mimicked by front panel LEDs: Input healthy In current limit Thermal control Over-temperature Digital outputs (no front panel LED) Fan Fail

Output current

Digital inputs: Inhibit / OVP reset

Programme down

Overvoltage Boost Active

Boost select

Digital inputs and outputs are isolated from the rectifier power output with optocouplers as described in section 4.2 below. The selection of the float or boost condition can be made in one of two ways; either the front panel switch can be used or the isolated digital input. If the front panel switch is set to boost the rectifier cannot be set to float using the digital input, so for remote control of this function the front panel switch should be set to float.

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4.2 Isolated Signals 4.2.1 Signals and LEDs The LEDs on the front panels of rectifiers fitted with signals cards are mimicked by isolated open collector outputs on the signals connector. The connectivity is shown in figure 4.1. The isolated signals are commoned on the signals connector pin identified as optos common (see tables in chapter 2). Additionally, the output healthy signal has a set of floating relay contacts. An isolated remote shutdown can be performed by applying a +5V source to the remote shutdown (+ve) pin with respect to remote shutdown (-ve). When the source is removed the rectifier automatically restarts. The shutdown port can also be used to reset the overvoltage latch circuitry providing the cause of the overvoltage has been removed. Simply applying the 5V signal and then removing it resets the overvoltage latch. Applying a +5V source to the programme down pin (only available on MRF28H**B and MRF28H**D models) will reduce the output voltage to 45.8V (22.9V for 27V product). Although the programme down voltage is factory set to 45.8V (22.9V for 27V product), it can be adjusted using potentiometer P16 on the signals card. For access to this see chapter 5.

4.2.2 Signals configuration The signals connectivity diagram (figure 4.1) shows that optionally the remote shutdown (-ve) pin can be connected to the optos common by closing DIL switch SW3C. Additionally, the programme down pin can be optionally connected to the remote shutdown (+ve) pin by closing DIL switch SW3D A summary of the signals card switch settings and other adjustments can be found in chapter 5.

Note Connector numbering shown in figure 4.1 is internal to the rectifier and different from the customer connect pins. For access to the signals shown in figure 4.1 consult the appropriate connections tables in chapter 2.

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5. Switch settings The rectifier operating mode switches are accessed through the window in the side face of the rectifier. Rectifier Operating Mode Switches Switch No

Switch set OFF

Switch set ON

Factory default

1

+ sense remote

+ sense local

ON

2

- sense remote

- sense local

ON

3

output set 54.5V

reduce output by 5V

OFF

4

normal voltage regulation

voltage droop regulation

OFF

5

constant current limit

foldback current limit

ON

Signal setting switches on the MRF28H**B version are accessible trough the rear panel grill. Signals Settings Switches SW3 (MRF28H**B units only) Factory default

Cct ref

Switch

switch set OFF

switch set ON

SW3A

1

Output current opto and overvoltage opto provide separate signals

Link output current opto output to overvoltage opto output

OFF

SW3B

2

Isolate remote shutdown opto

Connect remote shutdown opto output

ON

SW3C

3

Isolate remote shutdown opto common from opto common bus

Link remote shutdown opto output common to opto common bus

OFF

SW3D

4

Remote shutdown opto and programme down opto can be operated independantly

Link remote shutdown opto input to programme down opto input

OFF

SW3E

5

Enable overvoltage opto output

Disable overvoltage opto output

OFF

SW3F

6

54V operation

27V operation

set for unit type

Signals Settings Pots Cct ref

Function

P16

Set Programme Down Voltage

P17

Set Output Healthy Over-ride

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6. Thermal Control 6.1 Thermal Contol of Current Limit The MRF2800 series rectifiers are designed to supply 2.8kW output power up to a maximum ambient of 65C (55C for 27V). The current limit will operate slightly above the 2.8kW level, typically at 51A for a 54V unit (102A for a 27V unit). Thus demands for power up to the level of current limit will be met with a well regulated output voltage, and if system demand increases further the rectifier will provide a constant current by allowing its output voltage to fall. As the output voltage falls below 40V (20V for 27V rectifier) the output current may foldback or remain constant down to short circuit (see section 3.7.2 above). Should the rectifier be inadequately cooled due restricted airflow or too high an ambient temperature, its thermal protection circuit will limit the available output current. This condition will be indicated on units fitted with the extended signals by the yellow thermal control LED lighting, and by the thermal control opto output pulling low. The operation is summarised by the graphs below:

The operation of the circuit will be as follows: With the rectifier running in an inadequately cooled condition, one of the three internal sensors will eventually exceed its maximum designed run temperature of 90ºC. At this point the unit will enter the thermal control region, indicated by the thermal control LED lighting, and the available output current (i.e. the current limit value) will be reduced. However, if the system demand for current is less than the current limit point, no effect will be seen on the output voltage or current. If the unit continues to heat up, the available current will continue to reduce, eventually as far as 40A (80A for a 27V unit). If the system demand is greater than 40A (80A for a 27V unit), the rectifier's output current will be reduced to this value (causing the output voltage to drop) and the red current limit LED (enhanced alarms units) will light. If the unit continues to heat further the power conversion stage will be inhibited and the unit output will fall to zero: extended alarms units will have the red overtemperature LED lit as well as the thermal control LED. This condition will remain until the unit cools internally, then output power will be restored. Once output power is restored, the unit will heat up and the above process will repeat unless the cooling process is improved or the system demand is reduced. An example of the above process with numbers may help to clarify the operation of the thermal protection. An MRF28H54B rectifier is running at 54.5V and the system demand (load) is 45A. The unit is capable of supplying 51A. Due to inadequate cooling, the unit heats and the thermal control LED lights. At this point the unit continues to supply 54.5V at 45A, but the available output current is reduced. As the unit continues to heat, the available output current gradually reduces and eventually becomes 44.9A. At this point the current limit LED lights, the output current reduces to 44.9A and the output voltage falls below 54.5V: the unit power dissipation is reduced. If the unit continues to heat, the available current drops further and the output voltage falls correspondingly; the system receives less current from the rectifier and its power dissipation drops. At this point equilibrium may be reached with the output current limited to a value between 40A and 45A and the unit temperature stabilised. However, if the unit continues to heat further, the output current will be reduced to 40A (output voltage falls also) and further heating will switch off the output. When the output is switched off, the red overtemperature LED lights, the current limit LED goes off, but the thermal control LED remains on. When the output voltage reduces below 40V (20V for a 27V unit) the green output healthy LED (and output healthy relay) will switch off. This may occur when the unit is in current limit (depending on the value of load), or may not occur until the unit output is shut down due to overtemperature. Note: Units without enhanced alarms (MRF28H**A) will operate exactly as described above but without the LED indications on the front panel. These units have only the output healthy LED. 990-9153

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6.2 Thermal Control of Fan Speed The internal cooling fan operates at a variable speed, which is determined by internal temperatures of key components within the rectifier. These temperatures are a dependant upon both load and the external ambient i.e. the fan speed will increase in response to high loads and/or a raised ambient temperature. In average room ambient (25C) the fan will remain at minimum speed for loads of typically less than 75% of full load. To overcome potential problems associated with viscous fan bearing lubrication during low temperature starts, the fan is run at maximum speed after switch on for a period of 30 seconds.

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7. Safety and EMC 7. 1 Safety 7.1.1 CE Mark The rectifier is CE marked to the European Low Voltage Directive (LVD) 73/23/EEC amended by 93/68/EEC, relating to the Safety of Electrical Equipment. The rectifier is designed for incorporation within apparatus. For user safety, the enclosing apparatus must protect the user against accidental contact with any electrical hazard associated with the power supply and hot surfaces.

7.1.2 EN60950 / IEC950 The rectifier is approved to EN60950 / IEC950 and the requirements of these specifications must be met when installing the rectifier.

7.1.3 Energy and voltage hazard warnings The output power is greater than 240VA. All units other than rectifiers with part number suffix N are reliably SELV.

7.2 EMC The rectifier complies with the following: Conducted emission from the input terminals to meet EN55022 (Information technology equipment) level B. Conducted emissions from the load terminals as per EN 300 386-2. Radiated emission from the power supply to meet EN55022 (Information technology equipment) level "B". Input mains harmonics as per EN61000-3-2. Care must be taken when designing the shelf and rack wiring to ensure continued compliance of rectifiers with the above regulations. It is recommended that live, neutral and earth input wires are run together; also that positive and negative output busses are run adjacent. This reduces the likelihood of inadvertently creating loop antennas in the wiring. Experience shows that signal leads can radiate EMC, and it is recommended that all signal leads be screened. Additional filters in input or output power circuits should be used with care as resonances introduced can worsen the EMC performance of the rectifier(s).

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8. Maintenance The equipment supplied by APC is guaranteed against defective material and faulty manufacture for a period of 24 months from the date of despatch. In the case of material or components employed in the equipment but not manufactured by APC, we allow the customer the period of any guarantee extended to us. The equipment has been carefully inspected and submitted to comprehensive test at the factory prior to despatch. If, within the warranty period, any defect is discovered in the equipment in respect of material or workmanship and reasonably within our control, we undertake to make good the defect at our own expense subject to the standard conditions of sale. In exceptional circumstances and at the discretion of the Service Manager, a charge for labour and carriage costs incurred may be made. Our responsibility is in all cases limited to the cost of making good the defect in the equipment itself. The guarantee does not extend to third parties, nor does it apply to defects caused by abnormal conditions of working, accident, misuse, neglect or wear and tear. In the event of difficulty or apparent malfunction it is recommended that you contact the Service Department or your local Sales Engineer or Agent (if overseas) in the first instance. If a rectifier needs service, we recommend that it be returned to the Service Department at the address below, or to your local agent if overseas. Please ensure adequate care is taken with packing and arrange insurance cover against loss or damage in transit. If repairs are to be attempted by the customer these should be undertaken by competent personnel conversant with switch mode power supply technology. WARNING Hazardous voltages exist at many points within the equipment: test before touching. For service and repairs, return equipment to: The Service Department APC Wetherby Road Boroughbridge North Yorkshire United Kingdom YO51 9UY. Tel:+44 (0)1423 320000 Fax:+44 (0)1423 320033

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