Discrimination for single-phase residential

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dealova

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Hi all,

How to make partial or total discrimination for residential use ? I mean how to coordinate the circuit-breakers such a downstream fault (e.g. short-circuit), ONLY the circuit-breakers placed immediately upstream (D2) of the fault will trip. The main / incomer circuit-breaker (D1) remains closed.

My main / incomer (D1) circuit breaker has 25A rating, 4.5kA breaking capacity (60898), C Curve.

Any suggestion ?:|

 

dealova

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Someone has advice me that I should use 6kA on the D1 and use lesser rating (A) & 4.5kA on all D2 MCBs. Does it work ? If so, how about the tripping curve ?

 

tony.towa

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Looking at your second posting it would appear that you are considering both discrimination and cascading. Discrimination is to ensure that under fault conditions the circuit breaker directly upstream from the fault opens before the circuit breaker further upstream whereas cascading is a method of "increasing" the fault capability of the protective device downstream by utilising the characteristics of the devices upstream.

If you contact any of the major circuit breaker manufacturers (Merlin Gerin, Hager etc) they will send you full cascading and discrimination charts for their products.

 

dealova

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I have seen Merlin-Gerin literature about the discrimination setup but that's for three-phase which involved 3 levels (the Main Switchboard, the subdistribution boards, final distribution). There is no info on single-phase yet.

 

DonkeyDong

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Hi there,

I'll have a go (and be shot down) ; -)

You're break rating (4.5KA, 6KA, 9KA) doesn't come into discrimation (in simplicistic terms) - that is purely for the maximum fault current.

To ensure discrimation on MCBs, it is down to the tripping characteristics B/C/D (and their associated rating) - Although depending on the ratings/type of MCBs it can be very difficult/impossible to catagorically ensure you have discrimation - especially in domestic situations

Refer to the Appendix in the big red book for the tripping characteristics of MCBs

D.

 

dealova

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Not sure 'Big Red Book' holds much weight in Asia :|
Yeah, we don't have it here.

According to BS EN 60898, multiple of rated current :

B Type : 3 - 5 times

C Type : 5 - 10 times

D Type : 10 - 20 times

If it's down to the tripping characteristics, should I use B type for the downstream and C type (less sensitive) for the Upstream ?

 

DonkeyDong

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Oh...Asia.... but he is asking on a UK Forum :p

The only options you have to "play with" are MCB current rating, and type. (Just ensure your Zs still complies).

D.

 

dealova

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Oh...Asia.... but he is asking on a UK Forum :p
the house I build here must comply with the 17th Edition of the Wiring Regulations because the owner is Briton.

 
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the house I build here must comply with the 17th Edition of the Wiring Regulations because the owner is Briton.
The house you are working on is in the UK or the owner of the house is British (or both?)

If house in UK then you could do with a copy of the book if you are working as an electrician here. Are you familiar with the UK regs?

If you are not with an aproved scheme (or work for someone who is) the work needs notifying to Building Control at the local council.

 

dealova

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The house you are working on is in the UK or the owner of the house is British (or both?)If house in UK then you could do with a copy of the book if you are working as an electrician here. Are you familiar with the UK regs?

If you are not with an aproved scheme (or work for someone who is) the work needs notifying to Building Control at the local council.
The bungalow is in Asia, but the owner is British. He's trying to get a copy by himself. I just to make familiar to the rules.

 
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