ECN Forum Forums General Topics of the Trade General Discussion Area 2- 30amp receps

To play devil's advocate here:

In a commercial, or as stated above, lab environment, I would have no problem with this setup.

But in a home, I picture the frustrated homeowner driving over to the big box store and having the following conversation with the "expert":

Harry Homeowner: "Can you help me out? I have a welder and compressor in the garage and they keep tripping the circuit breaker."

Eddie Expert: "What size is the breaker?"

HH: "30 amps."

EE: "No problem. All you need to do is change it to 50 amps. We have those right here."

HH: "I'll take it."

One $25 breaker and possibly a house fire later, problem solved in both counts.

Admittedly, one would have to have a big welder and big compressor running full-tilt at the same time to cause significant heating of the {assumed} #10 feeder. But the repeated stress of overloading can trigger insulation failure down the road.

So, I would prefer to run two circuits just to be sure. If you have to lay pipe or fish NM to the location anyway, upsized pipe or two runs is not a lot more expense or labor than one run or pipe size.

Good question and the simple answer is they do not.

The NEC has a section devoted to welders that can be used if you want to use smaller conductors than would normally be used with a specific overcurrent device.

Basically they allow us to protect a conductor above its rated ampacity based on the duty cycle of the welder.

That does not mean we have to do it that way.

Bob

"All of us install multiple receptacle outlets on 15 and 20 amp circuits all the time with no idea at all what will be plugged into them."

Speak for yourself Bob... Doing Commercial Kitchen right now and asking the usual questions about equipment schedule, and use of certain areas. Knowing full well when the job gets trimmed out, I'll get the question about those "round single outlets", and why they can't be duplexes or quads. ('Cause the Inspector will want all of the equipment in place at trim out, and will look at all data plates...)

MX I could make that argument for every circuit in the panel. They also sell 30a single pole breakers that could get put on that pesky 14 ga circuit "that keeps tripping when we hook up the xmas lights".

If the wire was properly protected when it was installed and inspected I don't think we have any control over what another installer *might* do.

You do not install any branch circuits with more than one receptacle outlet?

Or do you just go back to each job and keep tabs on what gets plugged in after you leave?



Bob

iwire: If, rather than being cord and plug connected loads, the welder and compressor were both _hard wired_ onto the same circuit, would your answer be different?

My opinion is that if it can be reasonably anticipated that 210.19(A)(1) will be violated, then the installation is not up to code. This may not be enforceable, because as you note you can't determine ahead of time what will be plugged into the receptacles, but having 50A of load on a 30A circuit _is_ a code violation.

This does require a judgement: Do you as the installer think that the customer will be serious about not operating the two loads at the same time.

I know many people for whom the standard of circuit overload is 'does the breaker trip'. In the case of a welder and compressor on the same circuit, both very intermittent loads, I would not be surprised if you could have both devices 'on' and work with both effectively at the same time (welding, then using a grinder, then going back to welding, etc) without tripping the breaker too frequently......

-Jon

Bob, I ask the questions up front: (You've said you do the same...)
Use of space? (Electricaly)
Types of equipment, voltage, wattage, amperage...
And have the conversation up front, a little customer edjucation, about circuit limitations. Over-loads, nuisense tripping, loss of income due to outage because of those things... (The latter usually sells a circuit or two.) And when I come back, for that circuit thats tripped, they get the 'I told you so' when I find the extra commercial toaster, 3 20A printers, or the space heater under every other desk. Or the 20 extra track heads.... If it doesn't trip.... They were forewarned, conscience clean...

You are right, its a design choice, not a very good one IMO.

On 15-20a circuits its easy to assume that most types of general use items will only be a few amps. Could take 10-20 items to even get to 15A. On 30 amp equipment, you already know it is at least approaching 20a as a load. So with 2 items like that you know you are already approaching 40A right? Easy to assume without seeing a data plate> See 210.21(B)(2).

Jon, did you mean 210.20(A)(OCP-and a pretty clear violation for the reason stated above), on 210.19 (Conductors) you could just over-size the wire...


[This message has been edited by e57 (edited 03-25-2006).]

"Small conductors" get significant additional protection from 240.4(D). That is precisely because the installer has no control over what the user will plug in.
Bear in mind the OP said "receptacles".

e57: I actually meant 210.19, but was being sloppy; thinking 'why would anyone install 50A of conductors on a 30A breaker?' Being a couple of hours more awake, I realize that there are reasonable situations where one would do so

I think that you made a very good point which should impact the understanding of this sort of installation as a design issue: loads plugged into 30A receptacles tend to be 16A or larger; if the load required less than this it would be on a 15 or 20A cord. One could be virtually certain that 2 loads, each with a 30A cord cap, would total to more than 30A.

But when it comes down to it, what lots of us feel in our guts about this installation is embodied in 210.23(A)(2) which basically says that the _total_ rating of utilization equipment fastened in place on a circuit should not be more than 50% of the circuit capacity. A welder and an air compressor are both large loads that feel 'fastened in place' at least as much as a plug in range or dishwasher. However 210.23(A)(2) does not apply for several reasons; 1) It only applies when 'portable' equipment is supplied as well as the fastened in place loads, 2) It only applies to 15 and 20A branch circuits, 3) neither of these loads is likely really fastened in place.

As an aside, it seems to me that lots of aspects of circuit ratings are more about remaining consistent with the capabilities of old technology than what would be idea given new technology. Using current installation practices, it is entirely possible for a circuit to be overloaded without tripping the breaker; simply run the circuit at >80% capacity on a continuous basis. But it is entirely possible to build systems where it would be correct to say 'if the breaker doesn't trip, then the circuit is not overloaded.'

-Jon

gfretwell wrote:


True, but if you opened a panel door and saw 30 amp single pole breakers in a resi panel, that would trigger a red flag, right? Now look at the same panel, with 30, 40 or 50a double pole breakers, maybe labeled "garage", "welder", "compressor", etc. and I don't think your first thought would be to look for oversizing.

There is no preventative for what some fools will try to do, especially to their own service equipment. The main issue is the horrid advice given out at the big box stores. I have yet to hear of anyone who has gotten the right advice from one of those "experts."



Very true. That's the kind of situation that helps to keep the fire departments and fire restoration people (as well as EC's, of course) in business.