I'm thinking of installing mutiple 14-30R (dryer) receptacles in my garage for my 240V portable equipment (welder, compressor, box heater). The receptacles are dirt cheap, and there's a corded plug on every junk dryer.
Good question....after all, we have a "general purpose 110 plug," don't we?
Sure we do....for the smallest of our circuits those that are 110 volts and less then 15 amps. Increase the volts, increase the amps, and there's more energy being used. This means more damage when things go wrong.
So, to reduce the risk, and prevent actually creating a hazard by acidently supplying an appliance with the wrong "flavor" of electricity, we've developes a whole collection of plug types.
Every appliance -compresor, welder, whatever- has a nameplate that contains the information needed to size the circuit correctly. Besides "volts" and "amps," the plate may have phrases on it such as "duty cycle", "minimum circuit ampacity", "maximum fuse", and the like. This information, together with a copy of the code, tell you what size wire to use, the overload protection needed, etc.
A 30 amp breaker will let thirty amps through......maybe not a good thing if the appliance is only supposed to use 10! Use the larger breaker, and you've given away a large part of the protection the breaker is supposed to provide.
A 30 amp plug sugests that there is 30 amp wire behind it. Not really a good thing if there is really 15 amp wire, and a 50 amp breaker in the circuit instead.
Different appliances have differing electrical properties. Even a circuit perfectly designed for a 30 amp welder may be completely inadequate for a 30 amp air conditioner- even though the two use the same plug. This is because, besides the general circuit sizing rules, there are ten "exceptions" that are specific to different types of equipment.
I am sure that there are times where using two different apppliances on the same receptacle haas "worked fine for years." That is very possible, just as it is quite possible that the solution was absolutely correct.
Without knowing the details of all the equipment used, I just can't say. A plug is only one part of the system- and probably the least important part at that!
So I say, 'think it over.' Look at those nameplates, and the code book. Look at your supply wire, and the breaker that regulates it. Then decide.
Don't fall for the trap of "bigger is better." You wouldn't buy a pair of shoes two sizes too large!
#55747 - 09/05/0501:27 PMRe: General purpose 240V plug?
Also most 240V appliances do not use a N wire, 3 prong plugs. Personally I dont like general use 240V, I would rather tailor them to the equipment. As was stated all these devices require different wire and breaker sizes. An option might be to run pipe so they can be changed later. "Different appliances have differing electrical properties. Even a circuit perfectly designed for a 30 amp welder may be completely inadequate for a 30 amp air conditioner- even though the two use the same plug. This is because, besides the general circuit sizing rules, there are ten "exceptions" that are specific to different types of equipment." This is a good point especially with motors, welders etc that often have special requirements. Millions of circuits were installed from old fuse panels in garages for welding machines, 50A breaker, 10 wire and a 50A recept. Its a welder circuit (depending on the type of machine hooked to it) and not a general use 50A circuit like an AC or a pottery kiln would require. Heater too, maybe same breaker requirement but different wire, you could always use number 6 though and breaker it down for specific equipment I spose. I prefer to put large loads near the panel so its easy to run dedicated outlets or leave provisions for running new circuits as needed.
[This message has been edited by sberry27 (edited 09-05-2005).]
I am Code-savvy at this point (only a few months until I complete my apprenticeship )
Max max breaker sizes as per nameplate, and CEC rules are as follows: Welder: 21A primary current ---->42A max OCP Compressor: 15A FLA ----> 37.5A max breaker Box heater: 20A ----> mfr spec'd to use 6-30p or equivalent.
I forsee some other machines in the future... like a cabinet saw, mill/drill, horizontal bandsaw. They are all under 2HP, so they draw well under 15A at 240V, and have their own thermal overloads. Now, its common practice to use 5-15P corded equipment on 20A circuits even though it may draw much less than 15A. Would it then be allowable to put a ~7A load on a 20A/240V circuit?
In the ideal world it would be nice to have individual circuits for everything... but I'm a one-man shop with only so much money and time in the day. Seems like I only need as many circuits as there is stuff I can use at one time
#55749 - 09/05/0502:25 PMRe: General purpose 240V plug?
Just out of curiosity what model welder? Lincoln has some confusing ratings on some of their smaller ones but I am guessing a 175 class wire feeder. I like 10/30 on these as well as a 10/30 for the air comp. The comp would fly with a 12/30 circuit but likely the run is short and the 10 wire doesnt hurt anthing, good for motor starts. You are right about the availability of dryer cords, especially 3 wire, but they are not grounding type recepts. I would be tempted to leave some provisions for surface wireing in a working shop, makes it so easy to add as needed exactly where and when needed. You can plan a lot but I fid that machine locations dont always work out according to plans and when the wiring system is flexable there is a lot less temptation to leave things "as is" and just put up with it. Remember, God didnt set the machine in the first place you put it, it can be moved if its more convenient.
The reason I put the dryer plug on my welder was that was the only 240a circuit I had at the time. I really ecpected that I would be blowing fuses when I was on high power but it never happened. I made up a 50 foot 6ga SO "extension cord" from some that they ripped out of a computer room when that was outlawed. Years later when I got around to building a shop I stayed with the dryer receptacle. Using a dryer plug came in handy a number of times when I wanted to use my welder at a neighbor's house. Most people have an electric dryer receptacle.
#55751 - 09/05/0510:47 PMRe: General purpose 240V plug?