mccb Max zs 80% rule

Welchyboy1 · Mar 6, 2014

Hi all

I have an EICR underway and have to compare some ZS values for readings on some circuits protected by MCCB's

i have the manuf instructions with the max ZS values for the devices but do they have to be measured against the 80% value similiar to MCB's?

doesnt say anything in the instructions??

Many thanks

telectrix · Mar 6, 2014

treat it as any other circuit breaker.

Badged01 · Mar 6, 2014

Can only summize that its the 'ambient' Zs value they give for 'testing' the unit? If in doubt phone the manuf to confirm or if really stuck assume its not the 'ambient' value and apply the 80% rule!

Do the manuf quoted values differ wildly from the BGB?

Zebra Stripe · Mar 6, 2014

Oh dear, dig the new bread above>>>

Welchyboy1 · Mar 7, 2014

Thing is a few of the circuits are literally on the limit before applying any correction for temp rise so if this has not been allowed for then the circuits are not compliant which means changing the units which is ££££

But if i code this and im wrong im gonna look like a ****

Engineer54 · Mar 7, 2014

Welchyboy1 said:
Hi all

I have an EICR underway and have to compare some ZS values for readings on some circuits protected by MCCB's

i have the manuf instructions with the max ZS values for the devices but do they have to be measured against the 80% value similiar to MCB's?

doesnt say anything in the instructions??

Many thanks

If you have the manufactures max value, that's the value you should be working with, not the mythical 80% figure, they bandy around in the BGB!! Not that you'll find any values for MCCB's in the BGB, As every manufacturers data will be different, even between breakers of the same current value and model range!!

Never in fact, ever used/applied the 80% temperature multiplier, those i have checked have always complied with both values mind. ...Highly unlikely you are ever going to see any circuit working at, or even approaching anywhere near 70C!!!

shanky887614 · Mar 7, 2014

Engineer54 said:
If you have the manufactures max value, that's the value you should be working with, not the mythical 80% figure, they bandy around in the BGB!! Not that you'll find any values for MCCB's in the BGB, As every manufacturers data will be different, even between breakers of the same current value and model range!!

Never in fact, ever used/applied the 80% temperature multiplier, those i have checked have always complied with both values mind. ...Highly unlikely you are ever going to see any circuit working at, or even approaching anywhere near 70C!!!

Unless someone is bypassing meter with twin/flex lol