30a plug on a 10a device?

[Toller]

I guess I know the answer to these questions; I just want some reassurance that it is reasonable.

I am removing three circuits from my workshop and putting in a subpanel; the three are not adequate, and while I wish I had put a subpanel in much earlier, it is better later than never. I will end up with 2 240v circuits and 2 120v circuits.

1) My present 240v machines draw less then 10a, but I plan on replacing themeventually with ones that draw 18-20a, so I will use #10 and 30a breakers. Is it okay to use 30a outlets and put 30a plugs on my current machines?

2) I don't think I will ever use more than 20a on the two 240v machines and maybe 3a on the 120v at the same time, so a 50a breaker and #6 SER aluminum is adequate. Does that seem right? The run to the breaker box is 80'; any advantage to using #4 SER? It is not all that much more expensive, but I expect it is much more difficult to work with.

thanks.

[larryc]

It is allowable, but I would recommend just wiring up an adapter using a short piece of wire and extension cord ends, and leaving the plugs on your equipment as they are.

Check your wire sizing again. 50 amps requires 6 gauge copper, except with high temperature connections, which are not available in the home wiring section. 4 gauge aluminum should be your minimum wire size. Don't forget the anti-oxidant.

[gfretwell]

50a breakers will have 75c terminations, no matter where you buy them.

[Toller]

So you are saying I can use #6 aluminum (or #8 copper), right? I calculated that for #6 aluminum, 100', 43a, the voltage drop is only 2.5%. The circuit from the subpanel to the machine will only be 0.5%, so the voltage drop is okay.

Any reason to consider #4? The price isn't that much different; I am just concerned about working it the 80'.

[gfretwell]

The only reason you would consider the larger size is voltage drop. If you are using an appreciable part of the 50a that could be an issue. It really depends on what your expected load will really be.