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  1. raithrovers1

    NFPA 70E Clarification for UPS work

    I am trying to come up with a definitive answer to what PPE is required for my technicians to use when taking voltage measurements on a 480VAC input UPS less than 100KVA with a nominal 120VDC buss. Looking at the NFPA 70E tables it states that that panelboards or other electrical equipment rated...
  2. raithrovers1

    Magnetic field surrounding battery

    A technician of mine was performing battery maintenance on a UPS battery containing 2 strings of VRLA batteries. Each string had 40 jars, 240 Cells and were being float charged at approximately 530VDC. The battery is connected to a commercial type UPS (Powerware 9355) which has no isolation...
  3. raithrovers1

    208 through an isolation transformer

    Hopefully someone can help me understand the following: We have a UPS that was installed in the 80's. The input is from the A and B phase of a 3 phase 480/208 delta/star transformer at 208VAC. The UPS has an internal output isolation transformer on it. The plant take the A phase to neutral...
  4. raithrovers1

    PWM UPS fed by a constant voltage transformer (Ferro)

    We have a PWM UPS that replaced an old Ferro UPS. The site decided to re-use the bypass tarnsformer from the original UPS. This transformer is a ferroresonant constant voltage transformer. When commissioning the new UPS it was found that the UPS seems to work as designed. The problem only arises...
  5. raithrovers1

    Saw tooth UPS output

    I have a colleague who is working on a three phase UPS (MGE Comet). He attached his scope to the output and he is getting 480VAC phase to phase and a perfect sine wave which is as expected. He is reporting that when he goes from phase to neutral he gets a 277V saw-tooth. I do not have any...
  6. raithrovers1

    USA Voltages

    Guys I am a little embarassed to ask but I can't work this out at the moment (still new to the USA standard voltages!): I have a transformer with 240Vac primary to 240Vac/120Vac secondary. I have an unbalanced load. If I measure 50A on L1 with an amp clamp and 10A on L2, what is the primary...
  7. raithrovers1

    UPS output waveform

    I have an engineer that has come back from a site with the waveforms from a 50KVA UPS that were captured on his scope. The phase to phase waveform is sinusoidal without a great deal of distortion. The unit did not seem to be loaded anywhere near the system capabilities but the engineer did not...
  8. raithrovers1

    KVA vs KW again!!!

    Here we go again with another KVA vs KW problem! As a UPS engineer, I was always told that the output rating of most UPS systems is given at 0.8pf. I obviously would always check the specifications but in general it is between 0.8 an 0.9 for the industrial systems that I work on. When testing...
  9. raithrovers1

    RCD's in UPS distribution

    Hello Gents We have just replaced a 120kVA UPS on an oil & gas platform with a newer identical UPS. The original had 34 critical supplies fed from a distribution which all had 300mA RCD's on them. The new system had the same 34 MCB's but a were supplied with 30mA RCD's by mistake!! this was not...
  10. raithrovers1

    Stepped DC load calcs

    We have a DC system that requires a battery to supply the following stepped load: 1. 129kW for 15 minutes, then, 2. 106kW for 15 minutes, then, 3. 100kW for 60 minutes, then, 4. 18.5kW for 90 minutes I have contacted battery manufacturers and they disagree on the way the stepped load is...
  11. raithrovers1

    Calculating three phase power

    How can I calculate the output power from a 3 phase UPS with unbalanced loads? Load Voltage(Vrms)R-Y 409.8 Y-B 414.3 B-R 414.1 Load Voltage R-N 237.4 Y-N 238 B-N 239.7 Load Current(Arms) R 79 Y 27.7 B 41.3 N 68.4 Our engineer attached a Fluke scope meter to...
  12. raithrovers1

    UPS battery isolator shunt trip

    I was hoping somebody may shed some light on this problem: We are supplying our customer with an industrial UPS system. The battery (450Vdc) isolator requires an external tripping facility from volt free contacts. The UPS also requires to be able to be black started from the battery supply...
  13. raithrovers1

    Emergency generator cramking amps

    I am on site and they have a Em Gen module supplied by Aggreko. It is a Cummins genset 835kW. They went for a start a few days ago and it wouldn't start. I am on site to maintain their UPS systems and they asked if I would have a look. The batteries were at 24Vdc (should have been between 27.2V...

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