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[kdahm]

INTP - 20 Amp plug, 30 amp breaker??

That is A Bad Ideatm

If you really have a problem with the air compressor tripping the breaker on startup, go to a 20 amp slow blow breaker. If you want to use a 30 amp breaker, you MUST use a plug rated at 30 amps minimum.

Anything else is folly.

Sure, you can get away with it for a while. The NEC has a bit of slack built into it to allow for transient loads and natural variabilty. Responsible manufacturers put in a factor of safety because of variations in quality and to allow for end user error. One person, with one receptacle, can beat the odds temporarily.

One thousand people, each with one receptacle, will experience fires and shorts.

Sure, you know that the socket you labeled "30 amp" is a 20 amp socket. When you sell, will the next owner of the shop know? Will you remember to change the breaker, the receptacle, or the label before leaving? When a fire starts because he plugs in a 30 amp load, you will be at fault.

Look at the fire this weekend on a Canadian submarine fresh out of refurbishing. One officer died and at least six are seriously injured due to an electrical fire that started in one subpanel, spread to the main panel, and knocked out power to the entire boat. Millions of dollars damage, and hte investigation is just starting.

If the breaker is tripping, and it is the recommended size, find out why. Don't just flip a bigger breaker in and assume the problem is solved.

Finally, if you suggest someone else follow NEC and NEMA spec, don't turn around and tell them that you are disregarding it.

Respectfully
Karl

[ASKANDY]

He said he could get 60 amp 3 phase plugs free and the answer is still yes, you can run it single phase at 60 amps no problem.

A-

[kdahm]

Sorry for being unclear

My response was to INTP

I agree that 3 phase plugs can be wired as single phase. My only problem is that if the receptacle is wired single phase instead of three phase, a future user may plug in three phase equipment and expect it to work. I don't know enough to say if it could be a safety hazard, but it should be clearly labeled as single phase both in front and inside the box, possibly with a tag on the wiring.

I probably sound a bit paranoid about doing thing correctly, but I have tried to repair machinery at work that is 30-40 years old. Previous people working on them had changed the wiring so it didn't match the factory diagrams (when available), and nothing is ever labeled. After a few hours of tracing leads to find a problem, the urge to cause bodily damage to those who don't label things or don't do them correctly becomes appealing.

Personally, I'd rather have a SD 180 and wonder how to wire it, than not to have a SD180 (or anything close) and not need wiring.

Karl

[hankj]

A little water (or more fuel?) on the fire:

There is no NEMA spec to "follow". The National Electrical Manufacturer's Association (NEMA) has adopted a set of standards that define minimum production requirements. As a standard, it just exists. You can't "follow" it. NEMA references appear in the National Electric Code (NEC) because the National Fire Protection Assoctiation (NFPA - the publisher of the NEC) recognizes the validity of the standard.

I also read a statement somwhere in the replies that said something to the effect that the receptacle should always be rated higher than the expected load? If this is the case, why does the NEC allow 15A receptacles on branch circuits protectd with 20A breakers?

Ahh, the nuances!!

By the way, INTP, if you can rewire that compressor motor for 240V, it'd be happier!!

Hank

[kdahm]

15A Receptacles, 20 A Breakers

Because NEC expects that multiple point loads will be applied to the circuit, such that each receptacle is loaded to below 15A, but the total load on the circuit is below 20A? I would ecpect there is another provision that requires a 20A receptacle if a single load on the circuit is expected to exceed 15A.

You can follow the NEMA spec if you use a item in accordance with its manufactured intent and labeled rating. But that's just quibbling. Follow the code, and use products as labeled.

Besides, I'm a civil engineer, not an electrical one. If something is moving, it's got to be broken.

Karl

[INTP]

The compressor trips the breaker because it's a crappy single stage unit. Starting current is just over 50A, but only for a fraction of a second. Running current is 13A. FWIW, the circuit it is on has exactly one receptacle, something I forgot to mention earlier. The compressor will get replaced with a 240V 2-stage one, as other priorities are accomplished.

Karl, as I read what you're saying, the only thing we are seeing different is about the rating of the receptacles. I see your point, and I tried to express mine. I am certainly not trying to dissuade anyone from following your advice. Just my side of the discussion.


The 15A receptacle allowance on a 20A circuit is an interesting example of the ambiguity of the NEMA ratings. The NEMA rating can be seen as an indicator of the ampacity of the receptacle itself, or it can be seen as an indicator of the ampacity of the circuit. I interpret that in the 15A receptacle on the 20A circuit, it is the latter. In any case, I think the NEMA 'ratings' are ambiguous in some situations.

Perhaps we should all just hard-wire our 180SD's, since there doesn't seem to be a single phase, 240V, 3-conductor, 70A option (or none that I could find).

Barry

[hankj]

Hey, Karl,

I know some civil engineering stuff, like the "three guarantees for poured concrete": 1. It'll get hard. 2. It'll crack. 3. Nobody will steal it!!

Later guys. I'm gonna open a beer...

Hank

[INTP]

...
Later guys. I'm gonna open a beer...

Hank

Not fair at all. I'm still at work!

[Sberry]

I see this thread got pretty deep. 15 and 20A recepts,, hmm,, they are defined that way to allow the type of plug to be used. They want to make sure true 20A equipment doesnt get plugged in to less than 20A circuits. As for the wire having to match the breaker ampacity, no it doesnt. Read ART630.11 NEC specifically to welding machines. Some of them allow number 10 wire and 60A breakers. For the 180 in question here use a common 6-50-R recept and a P plug, number 8 wire and a 60A breaker as per the manual. As for the small air comp if this is a dedicated circuit (so you cannot plug other devices into it as was indicated) you can change the breaker to a 30 to keep it from tripping on startup. The motor has its own thermal to protect the wire from overload, the breakers purpose it to provide short circuit interuption.

[Bubba]

I don't know if Menards are national or just in the midwest but I got my connectors there. They were $10 each. Yes $10. I actually built a strip out
of 4 females of 6-50-R for the MM210, Dyn200DX, and the plasma.
I never use 2 at the same time so all could be wired in the same 40A circuit.
This way I have all plugged in. I know the Supply houses prices I started there myself......