240 volt Circuit Breaker Protection

[atthebeach]

I'm planning a small shop expansion which includes finally bringing 240 volt power into my shop. Every slot in the main breaker panel is full, but my electrician has proposed doubling up some of the 120 volt circuits with tandem breakers to make room for a 50 amp breaker that will feed a NEMA 6-50 outlet.

The welder I have in mind comes with a 6-50 plug, it is internally protected, and the manufacturer recommends a minimum 40 amp circuit. However, other equipment I am considering needs to be protected with a 30 amp breaker and some with a 20 amp breaker. Now, I can only use one piece of equipment at a time; so rather than running three new circuits, I am thinking about setting up a spider box with 30 amp and 20 amp breakers that when needed could be plugged into the 50 amp outlet. This is a temporary approach commonly used on construction sites, simple, and I believe safe, but probably not specified in the code. If I ever sold the house, I would simply unscrew the spider box from the wall and take it with me to avoid any code issues.

An alternative and more permanent approach would be to have the electrician install a double throw safety switch which can either feed the NEMA 6-50 outlet, or direct power to a load center box with 30 and 20 amp breakers and outlets. This would be a permanent installation, and I'm guessing would be allowed by code.

My preference is for the more permanent approach, but I would be interested in any comments you guys who do this for a living might have.

 

[pattenp]

Don't mess with switching between 50A outlet and load center. Just have all the outlets off the subpanel.

 

[zmaxmotorsports]

Why not just run a sub panel in the garage to feed everything off of?
Then you can run as many circuits off of it as you want.

 

[ard]

Why not just run a sub panel in the garage to feed everything off of?
Then you can run as many circuits off of it as you want.

+1

The subpanel in the garage is basically a fixed spiderbox

 

[sberry]

Use a 6 space panel, very cheap and can add breakers.

 

[sberry]

What welder are you getting?

An alternative and more permanent approach would be to have the electrician install a double throw safety switch which can either feed the NEMA 6-50 outlet, or direct power to a load center box with 30 and 20 amp breakers and outlets. This would be a permanent installation, and I'm guessing would be allowed by code.

How far is this? It is in the same structure? If it is close and can run a 6-3-WG cable from a 60A breaker to an 8 space panel they make just for this. I forget the model number and its not always on the box store shelf, they always have 6 space but if I was going to the trouble might want to include a 120V outlet for power tools too. Dedicated to a couple recepts I plugged any real power tools in to with a local breaker and new wire, maybe use the other space for parasitic stuff or a couple lights.

 

[theoldwizard1]

Use a 6 space panel, very cheap and can add breakers.

+2 ! Also, NM-B or SER is cheaper than SOOW cordage.

 

[atthebeach]

Thanks for all of the great responses! A sub panel does seem like the best approach, and including an additional 120 volt circuit would probably be wise.

 

[zmaxmotorsports]

Use a 6 space panel, very cheap and can add breakers.

Ive never seen the sense of wasting time money on a 6 space sub panel myself.
Bite the bullet and buy a main breaker panel with 20 or so spaces in it.

 

[rwilner]

Ive never seen the sense of wasting time money on a 6 space sub panel myself.
Bite the bullet and buy a main breaker panel with 20 or so spaces in it.

I agree with this, it is short $. you can get a square d homeline main breaker panel which includes a 30amp 2 pole breaker and some 20a single poles for like $50 at the depot. Don't forget to pick up a ground bar and make sure you don't bond the neutral.