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

NrVolts · Sep 22, 2011

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.

Knobhead · Sep 24, 2011

You won’t be able to do away with the neutral. If things do expand for your client then 4 kilns will be no problem to accommodate. The highest neutral currents you can expect assuming 40A per kiln is 80A. That is of course 2 kilns one phase and the other and 1 each on the others. There’s capacity for another kiln after that, I wouldn’t go beyond so that there’s capacity for ancillary equipment.

PM me your email address and I’ll send you a 3Ph Excel spreadsheet. Part of it calculates the neutral current in an un-balanced system. There’s a lot more to it than that.

Or you can use this
N = √((L1²+L2²+L3²)–((L1*L2)+(L1*L3)+(L2*L3)))

NrVolts · Sep 25, 2011

still no access to site.View attachment 7982 sorry this is sideways i cant see how to rotate it.
wont proceed any further till i get info on main board in main building like does it even have 3phase? i suspect it has but this hasnt even been investigated yet.
yes mr platty re reply 16, the 50 mm swa (supplied by the client)was put in by a colleague of mine who is quoting the works..
Really apprciate all the comments so far guys.especially the ammount of thought and time you guys have put in..thanks tony great info.bit beyond my capabilities but im sure others reading will find very useful.i guess this thread can be used for food for thought

hopefully the customer will go to an experienced contractor.i'l put in a close this thread comment if in 3-4 days from now the job has passed onto someone else.many thanks again.