Khanzada
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For the first item which is shower full 100% load 40A and the rest 56 x 0.4 = 21.6Would discrimination present an issue where 40A shower circuit is supplied from 63A MCB?
40+21.6= 61.6 A
Discuss Load calculations on three phase board in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net
For the first item which is shower full 100% load 40A and the rest 56 x 0.4 = 21.6Would discrimination present an issue where 40A shower circuit is supplied from 63A MCB?
For the first item which is shower full 100% load 40A and the rest 56 x 0.4 = 21.6
40+21.6= 61.6 A
I think as longer the load is not exceeding the main breaker load it’s ok , protective device must be equals or greater .I mean discrimination between supply MCB and shower MCB/RCBO. The reason for asking is that I believe the rule of thumb to achieve discrimination between MCBs is that upstream needs to be at least 2x the rating of that being supplied.
Happy to stand corrected.
If four residents on the same phase took a shower at the same time, this would be the case on a 125A incomer. Are there diversity rules to be applied between dwellings on the same phase though?As an apprentice my posts here should not be taken as advice, but as questions from someone who wishes to learn and what I'd really like to learn is how a 125A incomer might ever be considered suitable for a block of 12 flats?
Putting maximum demand to one side; if 4 residents happen to take a morning shower at the same time, that 125A incomer is going to be handling its full rated current before any other consumption is factored. If each flat were to draw an average 15A at any given time (not an unlikely situation), then the incomer is handling far in excess of its rated current.
It sounds like you are well out of your depth here.I think as longer the load is not exceeding the main breaker load it’s ok , protective device must be equals or greater .
I mean discrimination between supply MCB and shower MCB/RCBO. The reason for asking is that I believe the rule of thumb to achieve discrimination between MCBs is that upstream needs to be at least 2x the rating of that being supplied.
Happy to stand corrected.
Thank you for reply.
I spoke to costumer to fit 12ryefield board with 63A fuses , but he bought it live three phase board with 125A main switch rating and 12 , 63A MCBs to make the cost cheaper.
My question is if I installed that it will be ok for load demand .
Each pole of the isolator is rated at 125A so you can have loading of 125A per phase a total of 375A but the isolator will never see this, each pole will only carry 125A.It's been a long day, but at least I've come home to learn something at the end of it.
I'd thought that 125A 3 phase incomer was rated for 125A total, rather than per phase and I've some reading to do about discrimination as I'd read elsewhere that it could be achieved if upstream rating was at least 2x downstream.
Sorry to the OP for asking so many questions, but they were piling up in my mind last night and it seemed prudent to ask them for more than one reason.
It's been a long day, but at least I've come home to learn something at the end of it.
I'd thought that 125A 3 phase incomer was rated for 125A total, rather than per phase and I've some reading to do about discrimination as I'd read elsewhere that it could be achieved if upstream rating was at least 2x downstream.
Sorry to the OP for asking so many questions, but they were piling up in my mind last night and it seemed prudent to ask them for more than one reason.
Thank you for reply to my question, I calculated the load for all circuits after diversity 175A , in that case main incomer must be above the total load , I will change it to 250A .It's been a long day, but at least I've come home to learn something at the end of it.
I'd thought that 125A 3 phase incomer was rated for 125A total, rather than per phase and I've some reading to do about discrimination as I'd read elsewhere that it could be achieved if upstream rating was at least 2x downstream.
Sorry to the OP for asking so many questions, but they were piling up in my mind last night and it seemed prudent to ask them for more than one reason.
Reply to Load calculations on three phase board in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net
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