Brand new UPS trips RCD on main switchboard

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robfish

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#250858 28-May-2019 15:50

I have just connected a brand new Powercom Macan MRT 1000VA/1000W On Line UPS but when I turn it on (hold the on/off switch for 3 seconds) the RCD on the main switchboard trips after only 1 second.

Do I have to wait for the battery to fully charge or something?

Rob

dan

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#2247226 28-May-2019 15:52

its probably faulty - it should not be tripping your RCD (assuming your RCD has no issue)

robfish

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#2247259 28-May-2019 16:55

No this is the only thing which trips the RCD. If I put it on another circuit it trips that RCD too.
Supplier is happy to replace it or refund me the money (which is the option SWMBO prefers)

Rob

Zeon

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#2247270 28-May-2019 17:22

An RCD trips if the return path is through the earth - and presuming the housing of the UPS is earthed, could it be some loose cable inside? Probably best to get the supplier to review.

Speedtest 2019-10-14

richms

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#2247327 28-May-2019 18:58

Have you tried another mains cable into the input of the UPS?

Richard rich.ms

robfish

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#2247345 28-May-2019 19:40

Yes I am an electrician by trade. I am convinced that the UPS is faulty.

Rob

sparkz25

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#2247390 28-May-2019 22:20

robfish: Yes I am an electrician by trade. I am convinced that the UPS is faulty.

The only thing that I can think of is there is a short between neutral and earth some where in the unit or enough leakage to trip.

If its new i would take it back and get a new one.

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Aredwood

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#2247409 28-May-2019 22:40

Is the UPS output fully isolated from the incoming mains? (equivalent to an isolating transformer?) Or does it actually contain an MEN link on it's output terminals? As some appliances dont work properly if the neutral is not linked to the earth. (mostly gas appliances that use electronic flame sensing).

A local MEN link would be needed to cover the scenario where the input power cable gets unplugged. As the switchboard MEN link wont be available to the UPS anymore.

robfish

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#2247432 29-May-2019 06:19

Aredwood:As the switchboard MEN link wont be available to the UPS anymore.

You may be onto something here (with regard to an earthed neutral).

If, on the load side of an RCD, the neutral becomes earthed, it will trip.
Maybe this UPS is not designed to work with an RCD

Rob

Fred99

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#2247433 29-May-2019 06:34

Stumbled on this from Schneider - UPS causing RCD to trip seems to be a common enough problem for them to offer an faq (word doc)

This document examines one of the most common site issues with UPS systems, which is the tripping of the earth leakage protection, Residual Current Device (RCD) also known as an Earth Leakage Circuit Breaker (ELCB).

sparkz25

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#2247437 29-May-2019 06:37

Fred99:

Stumbled on this from Schneider - UPS causing RCD to trip seems to be a common enough problem for them to offer an faq (word doc)

That link does not work

Fred99

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#2247438 29-May-2019 06:40

sparkz25:

That link does not work

Link fixed.

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cyril7

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#2247441 29-May-2019 06:47

Hi, all switch mode supplies (including the one in the UPS) have filter capacitors from both P and N to E, there may also be MOV's, if those two caps have slightly different impedance at 50Hz, then you will have a differential current and trip the RCD. It might seem like a lot of variance in impedance is required, but infact it is not and the issue is common. Typically the variation is only enough to trip a 10mA RCD, but its not uncommon for this difference to be enough to trip a 30mA one. I might suggest you look at providing a seperate circuit for your UPS that does not go via an RCD. This is quite common practice for many products, especially those with motors (Fridge/heat pumps) that will often trip RCDs due to either start current leakage or in many modern inverter models the switch mode supply filter cap leakage as mentioned.

Cyril

robfish

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#2247447 29-May-2019 07:02

Thanks Cyril (and others).
I now have to think about the way forward.
I might even try a cheaper UPS for just my ONT, Edgerouter, switch and PoE switch (cameras and APs)

Rob