Add AC to 60 amp residence panel?

Status
Not open for further replies.
S

smallfish

Senior Member
Location
Detroit
Is there any code-acceptable way to add central air-conditioning to an existing 60-amp residential service?
The house has a Murray 60-amp panel with two fused pull-outs, one marked "Main" for the six 15-amp plug fuses below and another marked "Range" for the #8 conductor cable leading to the kitchen.
The 240-volt air conditioner is marked for a minimum circuit ampacity of 17.6 amps.
Thanks
 
Question just popped into my mind regarding this:

I have always did a load calc according to whatever is the adopted code at the time; however, is it legal to use the code that was in force at the time of the install instead?
 
Add AC to 60 amp residence panel

Add AC to 60 amp residence panel

Yes, to do a load calculation per 2008NEC, 220.83 (B) requires values and this is where I'm puzzled.
The AC unit has a minimum circuit ampacity of 17.6 amps @ 240 volts so I surmise its load at 100% is 4224 VA. The general lighting and general-use receptacle load is 4260 VA.
But here is where I have some trouble. If the existing panel has the six 15-amp circuits but the formula in 220.83 (B) requires loading each 2-wire, 20 amp small appliance circuit at 1500 VA each (of which the panel has none) how is it then determined what the load should be on the existing six 15-amp circuits?
Also how is the nameplate rating of the existing range determined? Can the nameplate be seen without moving the range from its position?
Thanks again.
 
Do the people a favor an request to update the service and panel. Then leave room for any future electrician to add circuits as needed.
 
smallfish said:
Is there any code-acceptable way to add central air-conditioning to an existing 60-amp residential service?
The house has a Murray 60-amp panel with two fused pull-outs, one marked "Main" for the six 15-amp plug fuses below and another marked "Range" for the #8 conductor cable leading to the kitchen.
The 240-volt air conditioner is marked for a minimum circuit ampacity of 17.6 amps.
Thanks
Click to expand...

Does the main does disconnect the Range as well as the others circuits? or just the 6-15 amp fuses
 
I don't know if the "Main" opens just the six circuits below or the six circuits below and the "Range" circuit.
 
Last edited:
smallfish said:
If the existing panel has the six 15-amp circuits but the formula in 220.83 (B) requires loading each 2-wire, 20 amp small appliance circuit at 1500 VA each (of which the panel has none) how is it then determined what the load should be on the existing six 15-amp circuits?
Click to expand...


In my opinion the 2 ea. small appliance circuits are used to cover the normal amount of small appliances used in the modern world.

People no longer live in 1950. Go into any home and you find a coffee maker, microwave, toaster oven, refrigerator, garbage disposal and who knows what all in the way of small appliances. They may not have the required small appliance circuits but they do have the small appliances. So allowing 3K va to the load on the service is still a good idea.

Will they allow central air on a 60 Amp panel? Get a permit and talk to the local authorities. They may allow some sort of grandfathering.
 
smallfish said:
Is there any code-acceptable way to add central air-conditioning to an existing 60-amp residential service?
The house has a Murray 60-amp panel with two fused pull-outs, one marked "Main" for the six 15-amp plug fuses below and another marked "Range" for the #8 conductor cable leading to the kitchen.
The 240-volt air conditioner is marked for a minimum circuit ampacity of 17.6 amps.
Thanks
Click to expand...


I did one of these a few years back and was able to use the range circuit as they were useing a gas range. ran new circuit conductors and correct fuses and things worked out. Total gas on large appliances (water heater, range and dryer).

The people were old and not much money to spend and there is probably a new owner for the house by now and an up-graded panel.
 
Dennis Alwon said:
Does the main does disconnect the Range as well as the others circuits? or just the 6-15 amp fuses
Click to expand...

It's been a while since I've seen an old 60 amp fuse panel but some of them had 2 lugs that were connected to the load side of the main pullout. Could that be used to feed a properly sized fused disconnect if the load calc allowed it.
My dad refered to it as pulling through the main.
 
qcroanoke said:
It's been a while since I've seen an old 60 amp fuse panel but some of them had 2 lugs that were connected to the load side of the main pullout. Could that be used to feed a properly sized fused disconnect if the load calc allowed it.
My dad refered to it as pulling through the main.
Click to expand...

Those are feed through lugs for installing sub panels.

Some only have one, so you can only have a 120 volt sub panel downstream from the main.

Some panels have a 60 amp main and a 40 amp range fuse set fed from the feeders, making the panel a 100 amp panel.

Some have the 60 amp main protecting the 40 amp range fuse, making it a 60 amp panel.

If one is lucky, the sticker for the panel should have a schematic on it.
 
This panel's max rating would be that of the main fuses as the range fuses are fed from the load side of the main. Also note the two feed through lugs. They are good for about a #10 wire and are fed from the main and with no other protection, protected only by the main.

View attachment 8676

A 'down and dirty' load calc would be to turn on everything in the house and see how much is being drawn. If it's close to maxing out, I don't think it would be a good idea to add 17 more amps. Even if you can justify it with load calcs from the NEC (a BARE MINIMUM standard) pushing these old panels to the limit may not be a good idea. I have seen the stabs on the main breakers overheat and arc just from normal every day use for a half century.

I doubt is was ever code to use fuses marked RANGE to supply some other load.
 
Status
Not open for further replies.
Top