Here's the setup:

30A receptacle on #10 wire with a 20A breaker protecting it, non-residential setting.

I maintain this isn't legal per 210.19 and 210.23(A)(1). The idea being that a 30 amp receptacle, when used as designed, guarantees that the circuit will be overloaded.

Have several people that disagree with me, arguing that the tripping of the breaker negates the overload, swear that they have had this install pass inspection.

Opinions?

-John

John,
Assuming this is a single receptacle then it is permitted by 210.21(B)(1).
Don

Don,

I saw that, but am I to interpret it to read that while I can never under-size a single receptacle, there's nothing to prohibit how large a receptacle you can put on a given circuit?

-John

John- I agree with Don. So if you install your 30a. single receptacle on a circuit rated for 15a. or 20a. you've not created a hazard but I don't see the advantage either.

John,
Yes.
Don

Table 210-21 (B)(3)is another example. For ranges and cooking appliances we use a 50 amp receptacle on a 40 amp circuit.

I didn't carefully read the articles I referenced earlier, and it appears neither of them applies.

While there doesn't seem to be anything directly prohibiting the oversize of a receptacle (and in some cases specifically allowing it), I don't understand how this doesn't violate 210.23 which supports my original argument(emphasis added): Certainly if a piece of equipment has a 30A cord-cap there is the real possibility it will draw more than 20A. If someone were to plug it into the available 30A receptacle, it would exceed the rating of the 20A breaker causing it to trip. This violates 210.23, correct?

Is it the responsibility of the person owning the equipment to ensure that a circuit is capable of handling the load they impose on it? Even if the receptacle on the circuit is designed for the rating of their equipment, and this receptacle is the only load served?

Or is it the responsibility of the installing electrician to ensure that using his installation as designed does not invariably creat a code violation?

-John

BigJohn ---

I agree with your reading. In general, 30amp recepts are not allowed on 20amp circuits.

Installing a single receptacle with an amp rating larger that the circuit supplying it is clearly permitted. How is installing a single 30 amp receptacle on a 20 amp circuit any different than installing ten 15 amp receptacles in a 15 amp circuit? Either way the circuit can be overloaded by the loads plugged in.

How do you connect a piece of portable equipment that requires a 70 amp circuit? A 100 amp device is the only option.

Curt

One hardwires the 70amp device. One does not use a 100amp plug.

---

One is required to comply with all of the sections of the code not just one.

George, why?

We regularly use 100 and 200 amp receptacles for mobile equipment.

Roger

George,
There is a lot of movable or portable equipment that require cord and plug connections. I have installed 400 amp cord connections for a portable rock crushing system.
Don

How about running only two legs of 277/480 plus PE to 3 parrallel 3 phase 50 A pin and sleeve receptacles? All of the devices intended to be plugged in, are single phase welders. I believe the breaker is either a 3 pole 30A or 50A. Commercial establishment.

Larry C

Edit to add last two words.

[This message has been edited by LarryC (edited 03-05-2007).]

I think it shouldn't happen. I agree that you are inviting overloading of the circuit which is a violation and hazard. If any piece of equipment with a 30 plug is rated over 16 amps 210.23(A)(1) will be violated.

The difference between 10-15amp recepts on a 15 amp circuit and a 30amp recept on a 20 amp circuit is that the likelyhood of the individual piece of equipment being plugged into the 30 amp recept exceeding the circuit rating is greater than the likelyhood that someone will plug in enough stuff to overload the circuit of the 10-15 amps recepts. If the odds were high that 10-15 amp recepts on a 15 amp circuit were overloaded the code wouldn't allow it. Of course in a non-residential setting you wouldn't put 10-15 amp recepts for specific loads on a single circuit if the loads would exceed the rating.

Don,

What are the odds that someone will plug in a different, higher load, piece of equipment where you installed the plug for the rock crushing equipment? I am assuming probably very low.

Steve,
You are correct that that circuit is not likely to be overloaded. My point was in reply to George's post that said larger circuits should be hard wired. That being said, it should be impossible to overload the conductors of a circuit with an oversize receptacle as the conductor should be protected at or below their ampacity and one of the purposes of the OCPD is to prevent conductor damage from overloads.
Don

George never worked in the computer biz. 60 and 100a 3p Russell Stoll plugs or IEC309s are very common under the floor. Back in the 20th century a decent sized tape drive controller (3803) would have a 100a plug on it. Want to hear the silly thing, they also had 14ga cables going out to the drives protected by the 100a breaker in the machine. I raised hell with IBM about it but they just said U/L listed it. It must be OK.
My worn out old war story about the flaming cable was on this machine.

I've had to hook up equipment that required 25A circuits, but came manufactured complete with special plugs that could only accept a maximum #12 cable. We ended up having to run #10 to boxes behind the rack and use a #12 jumper to connect the equipment.

While I disagree with others, I allow every professional to do this type of installation as they wish.

I only require that they accept all liability for the installation.

[This message has been edited by George (edited 03-09-2007).]

I appreciate the replies so far. I'm getting a lot on both sides of this argument: Two inspectors told me they wouldn't allow it, but couldn't cite any code off-hand to back up the rejection.

I've brought it up with a lot of experienced journeyman who take Don's position: An overload is impossible because the OCPD will open the circuit and prevent it.

While I agree that overloading the wiring is impossible, I don't read the definition of overload to be limited to wiring or connected appliances: The definition of "equipment" includeds "devices" and a circuit breaker is a device.

George, I'm curious to know, if you are in a professional capacity to restrict this practice, and you disagree with it, what makes you allow it?

-John

"I've had to hook up equipment that required 25A circuits, but came manufactured complete with special plugs that could only accept a maximum #12 cable. "

Thats kind of like my new MIG welder. (Hobart Handler 180) Has a 50amp 250v plug (NEMA 6-50P) and the owners manual states that it must be on a 50 amp circuit yet, the power cord is only 12 guage