PIGTAILING CIRCUITS IN FUSEABLE DISCONNECT FOR FURNACE QUESTIONS , AND OTHER , PLEASE

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Mattlong317

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Beech Grove, Indiana
Hey guys,
Almost 20 year experience guy here, but ran into a situation today that normally I would not think about doing, any and all help appreciated.
At an estimate today , in a very huge home, but outdated , the system was a weird mix of fuse disconnects , troughs, and breakers. Looked like commercial guys did work to the home post disable disconnect and updated to half breaker half fuse system. Very weird to me. Anyway homeowner ( H.O. ) has 20kw furnace , with only one circuit powering it , and jumpers from
60A breaker to 60A breaker in the furnace. 220V CIRCUIT BTW. Normally this requires 2 60A circuits to run the 20kw furnace. The furnace will not run correctly , keeps blowing fuses. My partner swears that insufficient power when motor starts can blow the fuses. Problem lies in that in the H.O electrical system no room for any tandem breakers and only 1 fuse disconnect opening . So question is , if we add another 60 amp circuit , can the original 60 Amp circuit, and our new 60 Amp circuit be pigtailed in the load center and be powered under the one fuse location ? ?
Also after doing some research , could this be a 25kw furnace with a 5kw element disconnected, and we may have mistaken #4 conductors that should have 80Amp fuses instead of 60Amp fuses, for 6 gauge wire, thus making the jumpers from breaker to breaker in furnace okay , and H.O. has wrongly been installing 60 Amp fuses ? I read a similar example online today.
Would the smartest option go with normal routine install 2 60Amp circuits , and pigtail them in the fuse disconnect , near main load center ? I have always understood " multitapping circuits " Is a code violation , but from research today I find that if breaker is designed for 2 conductors , or circuits are pigtails, tapping 2 circuits into one breaker/ fuse is perfectly fine??
Any and all help is highly appreciated.
 
AMMENDMENT to my post . Under NEC code for fixed heating appliance , if the furnace is 20kw , and the jumpers from breaker to breaker are correct , it would be this formula 20,000 / 240 = 83.3 x 1.25 ( for 125% ode ) = 104.16 amps for a single set of #2 conductors with a 110 amp fuse ? This maybe the way it is currently wired I suspect especially since the job was done by commercial electricians. I.e. 4 runs of pipe in basement , troughs etc.. . Please advise thank you .
 
Not 100% clear on what you are asking but, if I read correctly, you are asking about installing (2) #6 circuits and running them off (1) breaker. NEC 240.4 requires the conductors be protected at their ampacity. I see no exception to that which would be applicable in your situation so 1 #6 or 2 or 3 connected to one over-current device would require that OC device to be sized by the single #6 ampacity
 
Is this "furnace" load because of electric resistance heat strips? Often these are a separate circuit, especially if only used as emergency or auxiliary heat. What exactly are we calling a "furnace?" Do you have make and model number so we can get on the same page?
 
Hey guys thanks for the answers, got a little long winded and possibly confusing. .. but yes I was asking about 2 circuits on one breaker, pigtailed of course. And i do not have the model " furnace" , I know that would help quite a bit. I did more reading and it is model specific, but many furnaces can be ran either double service, i.e. two 6/2 romex circuits or can be powered single service as in #2 with a 100A breaker, and jumpers ran from breaker 1 to breaker 2 at the furnace disconnect. The furnace in question for a year so I'm fairly certain that's what the situation is . I had just never seen or heard of that before and I was wondering whether I should start from scratch with 2 new circuits. I will definitely check into the model and the heat strips . I'm fairly sure the homeowner has been installing 60A fuses in the disconnect attached to his panel instead of the 100A that should be there. Thanks again appreciate the comments.
 
If the main feed is only from a 60 amp breaker and you have ~20 kW of heat connected to it - 83 amps is going to trip that breaker on a pretty regular basis, regardless of what else is right or wrong.

What most call a 20 kW typically has a nameplate rating of 19.2 kW. 4.8 kW elements is typical, two of them on a 50 or 60 amp circuit is common, if there is a 50 and 60 amp breaker included in the unit the blower adds enough that the circuit supplying it needs to be 60 otherwise 50 is sufficient for the heat strips only.

What is typical for a single supply circuit is (4.8 kW = 20 amps) 20 amps x 4 = 80 amps x 1.25 = 100 amps plus blower which is usually 5 amps or less = 105 amps or so being minimum conductor ampacity required - which leads to overcurrent protection needing to be 110 amps.

110 amp breakers are usually expensive enough it is less costly to opt for running two 60 amp circuits even if the unit has a jumper assembly that makes it easy to install a single circuit for supply. Don't tell anyone that 100 amp breaker will usually never give you any trouble and is less costly and much more readily available then the 110amp , but to be purely code compliant it needs to be 110 amp breaker.
 
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