Tripping MCB

Obbit · May 7, 2014

Hi People.

We have a tripping MCB on a job from 8 years ago. This is the 3rd SMA inverter job to be doing this. One was because of a faulty cable in the inverter. Second, we never found out what it was, but did all tests and inspections on all connections and in the end changed the MCB to 20A from 16A (2.5mm cable) and haven't heard from her since (which I take as good news) . Now we have a third.

If any of you have tried to use the SMA helpline you'll know they aren't very helpful.

We have done a full spectrum of tests, r1+r2 (and N), IR, Zs, Ze. and a visual inspection on every connection. All is fine, but still the MCB trips after being on for a while (a few hours or a day). We have replaced the MCB but it still continues.

It's a SMA SB 2500 (so has a transformer).

Any ideas, or anyone come across this before?

Cheers

Pete999 · May 7, 2014

No such thing as r1+r2

telectrix · May 7, 2014

quite right pete, but not very helpful to OP. might be an idea to up the MCB to 20A as before. if it worked once........

Pete999 · May 7, 2014

Obbit said:
Hi People.

We have a tripping MCB on a job from 8 years ago. This is the 3rd SMA inverter job to be doing this. One was because of a faulty cable in the inverter. Second, we never found out what it was, but did all tests and inspections on all connections and in the end changed the MCB to 20A from 16A (2.5mm cable) and haven't heard from her since (which I take as good news) . Now we have a third.

If any of you have tried to use the SMA helpline you'll know they aren't very helpful.

We have done a full spectrum of tests, r1+r2 (and N), IR, Zs, Ze. and a visual inspection on every connection. All is fine, but still the MCB trips after being on for a while (a few hours or a day). We have replaced the MCB but it still continues.

It's a SMA SB 2500 (so has a transformer).

Any ideas, or anyone come across this before?

Cheers

Have you tried putting a clamp meter on the circuit to find out what the kit is pulling, could be inrush from the TX?

Gavin A · May 7, 2014

have you tested stuff like the varistors? I'm not sure, but maybe one of them on its way out could result in occasional fault currents or something. The other item that's got the potential to cause high currents would be capacitors.... never done it, but there's a guide here on how to test capacitors http://www.repairfaq.org/sam/captest.htm

interested in your results.

mayfair · May 7, 2014

A clamp meter could be your friend on this one !

Pete999 · May 7, 2014

The megger one that does multicores will give you an idea, not very accurate but quite handy, got one for a tenner + postage if you want one, pm me

camerabloke · May 7, 2014

I'll have it

Pete999 · May 7, 2014

Already got you one greedy git

Obbit · May 7, 2014

Thanks people.

I remember hearing that varistors are the first thing to go on inverters.
We upped the MCB to 20a. If if trips we'll have a little play around with the suggestions.
We're just avoiding replacing the inverter (out of warranty). I'll write up any interesting findings.