Sub-SubPanel or SubPanel?

[jeffg]

I am building an outbuilding that I am going to use as an office and hangout space for my kids. I am ready to pull power out to the building and I have a couple of options.

My house has a 200A main services, which then feeds two panels in the house and then one of those panels feeds a 100A subpanel in my shop, about 100' away. The new shop is about 20' away from the shop.

Would it be better to add another subpanel off of the shop (sub-subpanel) or would it be better to run a new subpanel directly off the main panel in the house? I have space for breakers in either one.

I would think that the shorter run would be better, as its well shorter, but the panel in the shop is on the opposite corner from the new office. It seems like it could be more complicated than just the straight run from the main panel.

Any benefit or problems one way or the other?

 

[86turbodsl]

You can do a sub panel off a subpanel, keep in mind that the smallest of the main breakers will be the limit of your current available.

 

[SarcasticDwarf]

You can do a sub panel off a subpanel, keep in mind that the smallest of the main breakers will be the limit of your current available.

This. Also, the next person that has to deal with it will thank you (or at least won't curse you).

 

[sberry]

You can do this either way and a lot would depend on the loads. For misc it wont matter. If they work hard with lotso heavy motor starts then I run another feed. For office and play a rather simple circuit may work. Only involves 20 ft of ditch.

 

[pattenp]

What will be the combined max loads of the 2 shops? Less than 100A I assume.

 

[jeffg]

The new office, will have electric heat and AC, as well as a light circuit and a circuit for outlets. The space is only 12x12, so I dont need much.


My consumption estimates are:
Heat - 1500 watts - 12.5A@120 (or 6.3A@240)
AC - 500 watts - 4.2A@120
TV - 80 watts - .7A@120
Fridge - 300-400 watts - 3.3A@120
LED Lighting - 60 watts - >1A@120
assume I somehow max out a 20A outlet circuit

41A@120 total, so I think a 60A@240 sub panel should work.

The biggest appliances in the shop are:
compressor - 28A@240
welder - 27A@240
Plus a handful of hand tools, some LED lights and a fan.

It seems like the consensus is to use the 100A sub panel in the shop as the source.

 

[wyliesdiesels]

The first step is determining your load calcs to make sure that the existing shop panel will be able to handle the additional load.

You havent listed loads for either space so its kinda hard to give an answer here without more info.

EDIT: posted this before the above comments showed up.

 

[alfredeneuman]

Heat - 1500 watts - 12.5A@120 (or 6.3A@240)
AC - 500 watts - 4.2A@120

You can eliminate the AC load from the calcs.
You won't be using the AC at the same time as the heater

 

[sberry]

I have wired at least 2 dozen garages where I put 60 breakers in. Couple with 5 hp comps and one with A.C. NEVER,,, NEVER had one cann with a trip. Once ran a welding shop and had 20 people living in the place from 100. At the time the inspector mentioned that i might have a trip issue, never did.

 

[sberry]

Only a couple times in my career did I run in to true overloaded service. One a tavern with a gob of ****, bunch of electric fryers, all 50A on a 200, probably 5 of them pluss the rest of the place which was busy on hot Friday night. The other was 60A fuses where they had all electric added on, cook, water heater, dryer, microwave, 3 teenagers.

 

[jeffg]

So... assuming I will likely never get to 60a actual load, am I good with 6/3 or should I step up to 4/3?

Since I have to go up and over the shop, the run is actually pretty close to 90 feet.

 

[AntonLargiader]

You’re unlikely to hit half that. I’d go with 6 and a 50A breaker, but you could make the case for smaller.

 

[wyliesdiesels]

So... assuming I will likely never get to 60a actual load, am I good with 6/3 or should I step up to 4/3?

Since I have to go up and over the shop, the run is actually pretty close to 90 feet.

If by 6/3 you mean NM-b aka Romex, you cant run that outdoors even in conduit...

 

[sberry]

It will work at 90 ft.