max load standard 100 A consumer unit (c/u)

[NrVolts]

hi there this is my first post so its likely i come across a bit unknowledgeable .ive got a customer who uses single phase furnaces for heating glass, ive been told that each furnace requires a 40A breaker.he intends to use 2 furnaces at first and then wants to add a third and possibly a forth.i know i should get the rated wattage for a clearer amperage of each unit, so i intend to find out tomorrow.i suspect if the 4 way c/u with 3 x40A plus 20A for a radial ring would overload the c/u on a standard 100A as the main switch is rated at 100A .im guessing each furnace would be about 35 amperes giving for 3 furnaces 105 amperes, and this doesnt even account for the 20A radial.so im guessing i will be having to tell him he can only run 2 furnaces and the 20A radial at once.the 20A is only for a few p.c.'s and display lighting.im worried if he uses 3 at once the c/u will probably ignite lol.done my 2330 but not much in it was about max load.

Thanks for reading.

 

[Paul.M]

Well this throws diversity straight out of the window if you know that all 3 possible 4 furnaces will be operating at the same time!

Is this a residential place or small commercial? What size are the main incomers? Is it possible (and cost affective) to get the DNO in to install 3 phase?

 

[Deleted member 19807]

If this is at a domestic property I believe the DNO should be contacted before they are connected to make sure they are happy with this load being on for the number of hours it will need to on for.

I read somwhere that the DNO use diversity for domestic supplies and although you may have a 100A fuse they only take in to account 9 to 10 Amps for their loading calcs per house, so if you pull 100A for any lenth of time it could overload the fuse at the substation if their is not enough overhead for extra loading.

 

[NrVolts]

reply for paul.m : its small commercial outbuilding.there is already one existing dis board in this outbuilding fed from the main building board on a 63 amp breaker.a new cable of 50 mm2 has been run to the outbuilding with the intention off adding 100 breaker in the main board .the new 50mm2 arrives at the main dis board but not terminated yet.i think i best say no to letting him run anymore than 2 at a time.i need to get the specs of the intended main supply board 15m away and the specific load of a furnace.its a real concern for me about possible high loads for let me get more info.thanks for replying will add more info tomorrow.

 

[NrVolts]

sorry forgot to confirm his furnaces are single phase ..so i would have to convince the client to change to 3ph arguing that its more economic in the long run.assuming he agrees i would have to advise him to get an much more experienced electrician than me to do the work.ive no experience wiring 3 phase and loads of this kind..i could breath a sigh of relief if that happens..

 

[Paul.M]

@ Nrvolts, What size cable is feeding the 63A and is it single phase? Why is there a dis board on a 100A being fed from a 63A board? Why 50mm tails feeding dis board?

Many of the lads on here can give you all the help you need to sort this out. Please get back with enough info after tomorrow, interesting one.

 

[Paul.M]

(posted at the same time)

sorry forgot to confirm his furnaces are single phase ..so i would have to convince the client to change to 3ph arguing that its more economic in the long run.assuming he agrees i would have to advise him to get an much more experienced electrician than me to do the work.ive no experience wiring 3 phase and loads of this kind..i could breath a sigh of relief if that happens..

Reason I said get a 3 phase supply is so he can 3 x 100A single phase supply so each furnace can be on its own phase, not for him to change them all to a 3 phase furnace.

 

[GLENNSPARK]

As far as i know you have to notify the DNO if high loads like this are placed on their supplies...........It sounds to me more like a commercial setup so as above.......a 3 phase supply may be more appropriate here............

 

[Paul.M]

Glennsparks my finger is getting saw hitting the "like" button after I read your posts.

Ps Glenn, shall we revive last nights thread on kitchen switches or leave it until the weekend? It's been a long day and tomorrow will be the same. See ya Saturday afternoon(ish).

 

[GLENNSPARK]

Glennsparks my finger is getting saw hitting the "like" button after I read your posts.

Ps Glenn, shall we revive last nights thread on kitchen switches or leave it until the weekend? It's been a long day and tomorrow will be the same. See ya Saturday afternoon(ish).

Well Paul...i aint got owt much on on saturday so that sounds fine to me mate. Thank you for the compliments as well mate. I try to give good posts.....sometimes i dont get it right but .....

 

[GLENNSPARK]

I`l be off in a minuite as its 6 am (again)...like every day tomorrow...lol...:rockon2:

 

[GLENNSPARK]

Just another thought here...single phase loads....so on a 3 phase supply he wants 4 furnices....so thats 4 loads on 3 phases....couldn`t/wouldn`t the 3 phases be "out of ballance" here?

 

[Paul.M]

Not at the Amps we are talking about I believe. I mean 40A tops each plus a skt circuit?

Besides 3 phase balancing? There's no 3 phase loads only single phase spread over 3. It's late, I'm up just before 6 as well, please correct my above post if I'm wrong lads.

 

[GLENNSPARK]

What i was thinking Paul was if 1 furnace was connected to each phase thats 3....so as there are 4 furnaces to connect up that would leave 1 to connect to any 1 of the three phases so if each furnace is 40A then one of the phases would have 80A on it....i might be seeing stars here though....lol.............:dizzy2:

 

[Paul.M]

If he/DNO install a 3 phase supply/board, each phase is 100A main fuse.

Glenn go to bed, its too late for this. See you tomorrow if I have the energy to log on .