Tripping the breaker

Hi all,

Not a PLC fault, an electrical one. But the electricity supplies a PLC. So I guess it counts.

I have a C63 3 phase MCB providing the circuit protection to a large industrial unit, loads of sockets, things this and that. I have a single phase robot controller plugged into the 13A ring in the building, as it is designed to be. On this I also have a few things wired up through other circuit breakers. A single phase C4 circuit breaker feeds some stuff, when I cause a short circuit on this (for testing of the systems reactions) it trips the C4 but also trips the C63. I assume this is because of load imbalance.

However, how do I stop this from happening? I don't really want to change the C63 breaker unless I absolutely have to as the landlord will have to do it I expect. I imagine it is just a design problem. Or an education problem on my behalf. Should I need a D type or B type breaker or am I missing the problem?

Any help on a postcard appreciated. Circuit breaker pictures attached if this helps.

A short tripping a 4A breaker that also trips a 63A breaker is either a massive short or I would look elsewhere.

When the machine is running what is the measured current going through C63? If it is close to the limit then the small short could cause a problem.

If your amp meter has a peak see if the current through C63 goes too high when it trips (you may have to test on all 3 leads to find the one)

Directly above C63 in the photo is that part of another breaker, a fill-in plate or possibly a ground fault part of C63? If it is a ground fault it would trip immediately.

If your short circuit current is greater than 63 x 5 = 315A then both breakers will trip instantaneously. You "might" correct this by changing the 63A breaker to type D which will trip instantaneously at 630A

I_Automation said:

A short tripping a 4A breaker that also trips a 63A breaker is either a massive short or I would look elsewhere.

When the machine is running what is the measured current going through C63? If it is close to the limit then the small short could cause a problem.

If your amp meter has a peak see if the current through C63 goes too high when it trips (you may have to test on all 3 leads to find the one)

Directly above C63 in the photo is that part of another breaker, a fill-in plate or possibly a ground fault part of C63? If it is a ground fault it would trip immediately.

Click to expand...

L D[AR2 said:

If your short circuit current is greater than 63 x 5 = 315A then both breakers will trip instantaneously. You "might" correct this by changing the 63A breaker to type D which will trip instantaneously at 630A

Click to expand...

Hmm. I will have to ask the guy doing the testing what he did then. Will also get the info on the board. Not there this week and I didn't do the testing, just heard the problem and thought... try a B type instead of the C, must have misunderstood the problem. Chinese whispers all around.

we had this issue years ago.
I would look at the neutral wiring for the breaker and the ground wiring for the circuit.
james

James Mcquade said:

we had this issue years ago.
I would look at the neutral wiring for the breaker and the ground wiring for the circuit.
james

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When you say check... Any pointers? No need for an electrical lesson but anything you remember being an issue?

we found 2 issues.
the neutral was loose and the ground was missing. I cannot remember all the other details as to why.
james

James Mcquade said:

we found 2 issues.
the neutral was loose and the ground was missing. I cannot remember all the other details as to why.
james

Click to expand...

Nice one. I'll be back there next week I'll check it all out

Just remember to turn the power to the panel off first !
if that is not allowed, suit up with your ppe, insulated tools, and the correct face ppe designed for arc flash. Safety first.
james

Oh, that's not a real Circuit Breaker you need for Branch Protection, just a supplementary protector is all.

I see this stuff all over the place where it looks like a CB, therefore it is a CB...


Big differences.

padees said:

Oh, that's not a real Circuit Breaker you need for Branch Protection, just a supplementary protector is all.

Click to expand...

OK cool, what do you mean? And what do I need in this case?

James Mcquade said:

Just remember to turn the power to the panel off first !
if that is not allowed, suit up with your ppe, insulated tools, and the correct face ppe designed for arc flash. Safety first.
james

Click to expand...

Of course

please keep us informed as to what you find,
james

Does C63 feed a transformer? If so, is there secondary xfrm circuit protection? If not add some. Also C63 appears to be labelled as Surge Protection. Hmmm. Upstream protection? Good luck