D curve breaker

[kzzam]

I have been asked by a customer to solve a problem, he has a 3 phase 20A D curve breaker supplying 3 single phase breakers 2 x 6A and 1 x 2A. The 6A breakers are supplying 2 pumps with a load of about 4A each. When 1 of the pumps are turned on, the 20A trips. Any ideas why? The earth loop impedance is quite high but still within regs. Can this be the problem.

 

[telectrix]

what size cable from 20A CB to the 6A and 2A?

 

[trev]

Is this either of the pumps tripping the 20A or just one of them?
What tests have you done apart from EFLI?

 

[Pete999]

When you say the ELI is high but within the Regs, what is the ELI? and on what circuits?

 

[Silly Sausage]

What is this 20A D type breaker's purpose in life?
Can't you just get rid?

 

[kzzam]

I suggested getting rid. It's a bit of a bodge. Trying to convince him to get a new system. If I can solve this he probably will. Not sure of readings another electrician took the readings. I am trying to do this over the phone! as he is considerable distance away. Cable is 6mm and 4 mm, either pumps trip the breaker. Insulation resistance of cable has been done is ok. I know I am taking someone's word for it. Just wanted to sound it out on here. 2A circuit isn't being used.

 

[kzzam]

I believe ELI is 0.5 ohms, reading table 41.3 maximum Zs is 0.57.

 

[Pete999]

So you can't say in all honesty what the ELI really is, not having a go but you really need to get the exact reading for any opinion to be formed as to the problem, don't forget that table is for design purposes, might be better to use the table in the OSG, or apply the correction factor.

 

[kzzam]

Yes I agree. Just wondering why the 20A trips and not the smaller c type breakers. I will have to go and test it all myself. I was hoping I could give him some sort of answer then when I got there I could rip it out.

 

[trev]

So what you do is tell him that there are a number of possibilities but you'll have a definite answer for him after you've concluded your testing.

 

[kzzam]

Yeah ok I was just being lazy. Busted.

 

[trev]

Not the intention of busting you mate, I meant that you'll look better because by saying that you're also saying that you're not going to baffle him with bullpoop over the possibilities and also that the answer you give him will be the right one.

 

[Darkwood]

What size motors are they? 4amp rating seems an oddball figure.
How long is the run from the 20amp breaker?


TBH you don't seem to have half the info needed here so not really any help we can give you, either go to site and evaluate or speak with this 'other' Electrician who has taken the ELI readings and get the relevant info' - you can't solve a problem with 'I think', 'Not sure' and assumptions.

 

[Brightspark2]

What size motors are they? 4amp rating seems an oddball figure.
How long is the run from the 20amp breaker?


TBH you don't seem to have half the info needed here so not really any help we can give you, either go to site and evaluate or speak with this 'other' Electrician who has taken the ELI readings and get the relevant info' - you can't solve a problem with 'I think', 'Not sure' and assumptions.

I think you can...


actually I'm not sure...


I'm just making assumptions...