Add a range? Service amps not enough

[Mr. Serious]

I would like some advice on how to proceed here.

Customer called, converting gas range to electric. I went out to take a look. 100A service, and he has a new 13.5 kW electric range. I told him I would do a load calculation and see if the existing service would support an electric range.

gas heat, gas water heater, electric dryer, air conditioning (18.1 amps MCA on the outdoor unit)
I get about 110 amps of load using the standard load calculation. I'm assuming a dishwasher, disposal, and range hood are the only built-in appliances.

I had a job like this before, where the customer wanted to add a hot tub and it put his service at 103 or 104 amps of load, and I refused to do that job, but that time, there were other things wrong also, and overall it didn't seem to be one that I could do without spending more money than the customer probably wanted.

In this case, the job itself looks simple enough, the existing electrical system is old, but it hasn't been messed with and is in good condition. But I'm still leery of adding load to make the total load calculation come to 110 amps on a 100 amp service. Perhaps the alternative method of calculating load would allow it? I don't know much about that one.

 

[Dennis Alwon]

Did you do an optional calc? What did you use as the range kw for the standard calc.

 

[Mr. Serious]

Range kW, I believe since the name plate says 13.5 kW, we are allowed to derate to 8.8 kW. That's what I used.

I didn't do the optional calc. That's what I meant by "alternative method of calculating." Does it usually come out lower?

 

[Dennis Alwon]

Yes, almost always. What is the sq.ft of the house

 

[Mr. Serious]

1218 square feet.

 

[Mr. Serious]

(Edited) I think I see the optional calc starts with section 220.80 in the NEC.

 

[Dennis Alwon]

So I used 1200 sq.ft and a microwave at 1600 , dw at 1200 and I get 95 amps on optional and 109 on standard

 

[Dennis Alwon]

The optional calc is the part starting at 220.83 in the NEC, right?

220.83 for existing... For existing I got 90 amps

 

[Mr. Serious]

I edited that comment to say 220.80 instead of 220.83 after I looked through the code book some more.

I need to build myself a spreadsheet for the optional calculation. Thank you for your help. I think I will proceed in this case by letting the customer know that the service is barely large enough, but would definitely have to be upgraded if he adds anything else in the future.

 

[Dsg319]

Mike Holt tool box is an awesome app with a built in service load calculation which I’m pretty certain is the optional method.

Great time saver for actually doing it in the real world and not studying or taking a test.

 

[Mr. Serious]

Mike Holt tool box is an awesome app with a built in service load calculation which I’m pretty certain is the optional method.

Great time saver for actually doing it in the real world and not studying or taking a test.

I already have a spreadsheet that I created for doing the standard method, saves a lot of time over doing it all by hand.

Thank you for the tip.

 

[rambojoe]

Load calc aside, did you turn everything on and plug in appliances to see what its really pulling?

 

[drcampbell]

Is there any unused capacity, such as it actually being a 125-amp panel?

 

[Rick 0920]

Sell the customer a 200 amp upgrade and make some $$$$ on the job!

 

[jaggedben]

If you have meter data there's also 220.87. Or just look at the data for perspective.

It's probably fine, my gut feeling. The heating elements on both a dryer and a range cycle on and off during use so are unlikely to be on simultaneously very long.