Knots thread: 20A recep. on 50A branch
Guys,
See this thread on http://forums.taunton.com/fw-knots/messages/?msg=33694.1
Someone claiming to be a “code inspector in 5 states” is claiming that is it OK to put multiple 20A receptacles on a 50A branch; e.g., 3 20A duplexes.
I’ve never heard of this, and can’t see how it woudln’t be downright dangerous. And 210-21(b)(3) is clear on the matter. Any even brought this up on Mike Holt’s forum, and they agree the table says what the table says.
Still, he’s maintaining he’s right. He’s out to lunch on this, right?
Replies
I'm an EE as well. I've been following that thread, and I'm with you on this one. This particular entry in that thread was really making me wonder. http://forums.taunton.com/n/mb/message.asp?webtag=fw-knots&msg=33694.21
Edited 2/2/2006 11:15 pm ET by Stuart
When I first read your post, I assumed that maybe the man was confusing branch ckts. with submains.
So I read through the entire thread and he confirmed that he was an expert. (?).
Now I'm a builder and not a licensed electrician, but I'm pretty familiar with residential and some industrial wiring and attendant devices. But what I'd be interested in learning is why he loaded his shop with arc fault protection....not being facetious....just wonder about the reasoning.
AFI will trip with a standard electric motor that powers most shop tools, won't it? I know nothing about it, but when I tried running my circular saw off a house circuit recently, it kept tripping the safety. The elec. said the AFI would not power my saw."he...never charged nothing for his preaching, and it was worth it, too" - Mark Twain
I think that guy is way out in the weeds. First problem is he is an engineer. They have a different way of looking at things. Next problem is he states that a dead short on a 15 amp breaker will not trip, but an overload will. Then he says he is a practicing electrician, which exactly means what? Then he says he is a code inspector, which may be true, or not, because this is afterall the internet and we can be who we want if we can be convincing enough. He's just dangerous, and bizarre.
two ways look at it. we know a 15 amp rec. will not over load a 50 amp line but I still would was a 15 circuit breaker even if he was using 50 amp wire. but then the wire would not fit in the rec or circuit breaker. Isnt 50 amp like 8 gauge?. 2+3=7
>>Isnt 50 amp like 8 gauge?6 gauge
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Sojourners: Christians for Justice and Peace
">>Isnt 50 amp like 8 gauge?6 gauge"#8 rated for 50 amps if you can use the 75 degree column. Which you can't if you use NM cable, but if you use conduit and run THHW you can.
But would you put a 20 amp outlet on it?
Yes. This is very basic. Every house has 15A receptacles in the kitchen, on a 20A breaker and (hopefully) 20A romex (12 ga. in most locations). This is perfectly legal and perfectly safe.
The simple logic is this: the breaker is ONLY there to protect the wires from the breaker to the outlet, so they don't get overloaded and burn the house down. Thus the requirement for matching the wire size to the breaker. The breaker DOES NOT and CANNOT protect anything you plug into the outlet because there is nothing to prevent you from plugging, let's say, a clock with 20ga. cord into a 15A outlet.
The requirement that the outlet itself be of no higher amp rating than the breaker/romex is simply to prevent the user from plugging in something too big that will pop the breaker every time.
Ground fault and arc fault protection are a separate issue.
DG/Builder
Edited 2/3/2006 12:08 pm ET by dgbldr
"Yes. This is very basic. Every house has 15A receptacles in the kitchen, on a 20A breaker and (hopefully) 20A romex (12 ga. in most locations). This is perfectly legal and perfectly safe.
The simple logic is this: the breaker is ONLY there to protect the wires from the breaker to the outlet, so they don't get overloaded and burn the house down. Thus the requirement for matching the wire size to the breaker. The breaker DOES NOT and CANNOT protect anything you plug into the outlet because there is nothing to prevent you from plugging, let's say, a clock with 20ga. cord into a 15A outlet. "
I think the flaw in your logic is that in your example, 12ga wire is used, which is generally capable of handling the 20A. Therefore even under maximum draw, the wires will not melt down regardless of what the recepticle itself is rated for.
In this case under discussion, the 6ga (or 8ga) wire cannot be run to the recepticle, because the outlet itself is not capable of handling a wire that fat. Generally the max conductor size for recepticles is 10ga.
That's besides the point. The question was whether it's legal and safe. Yes it is.
By the way, there are 220V single phase 20A receptacles that can be outfitted with lugs that will handle large gauge wire. See your friendly local industrial electrician.
DG/Builder
I guess you could take that thought a little further, the breaker would not be protecting the recptacle either . I would expect that is why we put them in boxes and cover them with the covers. Do they still allow those wooden covers? I have not looked to see if the newer ones have a metal backing.
"I guess you could take that thought a little further, the breaker would not be protecting the recptacle either . I would expect that is why we put them in boxes and cover them with the covers. Do they still allow those wooden covers? I have not looked to see if the newer ones have a metal backing."
No, the outlet does not have and does not need protection, other than the built-in coding (plug pin size/shape/position). Protection against what? Overcurrent? A 15A outlet is safe up to 15A with plenty margin. The only way to connect a 20A appliance to it is to cut the plug off the 20A appliance and put a 15A plug on it. That IS against code and more importantly, against common sense.
There are several reasons for putting receptacles in boxes, but none of them have to do with the subject of this thred.
DG/Builder
You must not be very creative in how to stress the system. Take that triple tap extension cord and plug three items into it. Stick one of those neat six hole cover plate type adapters in there. Put one of the neat power strips that do not have protection and load it up. The insertion point is the most vulnerable part of the circuit I would think. You do not need a 20 amp appliance to come up with an overload.
I think you will pull more than what a 15 amp recpt. is designed for and NEC be damned ( I realize we are in the world of UL at this juncture). Like you said not smart but the world is overly blessed with less than smart folks though.
The simple logic is this: the breaker is ONLY there to protect the wires from the breaker to the outlet, so they don't get overloaded and burn the house down. Thus the requirement for matching the wire size to the breaker. The breaker DOES NOT and CANNOT protect anything you plug into the outlet ...
That's NOT true, although it is an oft-quote "internet myth" about the NEC. There are plenty of places in the NEC which defiend circumstances where the branch circuit OCPD protects things attached to receptacles; e.g, 240-4 and 422-11. Do you have a copy of the NEC?
This is the reason why, in 210-21, the NEC prohibits receptacles from being installed on branch circuits with ampacities much higher than the receptacle. It ensures that equipment won't be supplied by a branch circuit with overcurrent protection higher than that for which it has been safely designed.
there is nothing to prevent you from plugging, let's say, a clock with 20ga. cord into a 15A outlet.
Yes there is: the NEC. It says one must follow the ampacitiy tables for flexible cord in 400-5, unless it is part of a listed piece of equipment: in that case, the equipment has been verified by UL or another lab to be safe when attached to any branch circuit that its plug will fit into; again, this is why 210-21 prohibits a 15A receptacle on a 50A branch, because the listed equipment would not have been tested for safe operation on a 50A circuit. Note also that ampacities for flexible cords are not the same as those for NM cable, but are defined separately.
The requirement that the outlet itself be of no higher amp rating than the breaker/romex ...
There is no such requirement. One may use 50A receptacles on 40A circuits, per 210-21(b)(3). For the case of a single receptacle on a dedicated branch, the receptacle may be larger than the branch circuit rating. In some cases, this "upsizing" is necessary; e.g., in order that the plug and receptacle horsepower ratings match that of the motor with whihc they are used.
thought maybe dqbldr and decolores were the same 'mythical expert' at first, but the troll signatures (start, number of posts, etc.) do not quite match.
If either of them tried to spew misinformation like they do in the company I work at, they would be shown the door fairly rapidly, unless they were promoted to management<G>.
dgbldr, you are correct in using 15 amp receptacles on a 20 amp circuit. It is allowed by NEC. But not in using them on 30, 40 or 50 amp circuits! Here is the NEC data posted by BarryO in the Knots discussion 33694.26 . 210-21. Outlet Devices.
(b) Receptacles.
(3) Where connected to a branch circuit supplying two or more receptacles or outlets, receptacle ratings shall conform to the values listed in Table 210-21(b)(3), or, where larger than 50 amperes, the receptacle rating shall not be less than the branch-circuit rating.Table 210-21(b)(3). Receptacle Ratings for Various Size CircuitsCircuit Rating Receptacle Rating
(Amperes) (amperes) 15 Not over 15 20 15 or 20 30 30 40 40 or 50 50 50And yes, I have seen three (3) irons plugged into one outlet using a tripple tap extension cord, 3KW on a 20 amp circuit. I'm glad it wasn't a 50 amp circuit! The extension cord would have been the fuseable link!Frank DuValYou can never make something foolproof because fools are so ingenious.
I'm no electrician, but it seems to me that putting a 15 amp recepticle on a 50 amp breaker and running heavy 6 guage wire between them is a REALLY BAD idea.My reasoning is this: Wouldn't the recepticle itself be the weak point? Say you load up the outlet with three 15 amp space heaters and turn them all on at the same time. The 50 amp breaker would not trip (because you are only using 45 amps). The 6 guage wire would not melt (because it is rated to carry a 50 amp load). The heaters themselves would not fry (they are loving pulling every possible amp of juice from that fat supply). BUT the outlet itself is going to get mighty hot, melt, burn your house down, cheat on your wife, and poke out your eye. Why? Because the outlet is only rated to have 15 amps coursing through it. Instead it has got triple that load (three 15 amp heaters = 45 amps). The breaker (which would normally protect a situation like this from occuring) will not pop because it will only pop if the load exceeds 50 amps.--Andy
Andy,
Maybe you're not an electrician, but your instincts and understanding of the theory underlying the rules are spot-on. The scenario you describe is one example of why the "wise men" (i.e., the NFPA committees charged with writing the NEC), don't allow little receptacles on big circuits.
Exactly.But I want to make one minor clarification. Does not affect this discussion, but it is common item for discussion.The common duplex 15 amp receptacle, while rated for only 15 amps max at each connection is rated for a total of 20 amps. That is 15 amps in one, 5 in the other, 10 and 10, etc. Or 20 amps feed through to the next receptacle if wired in a diasy chain. That is why a 20 amp circuit can have 15 amp receptacles as long as you have more than one.
You would have to pigtail off the heavy wire to the receptical. Aint happening here tho.
"... he is an engineer.... he is a practicing electrician... he is a code inspector..."
The problem is the he is most likely none of the above, but rather just a liar and a pretender. Plenty of those on all of the forums. However, if were to dare point this out, call the BS what it is, you will be villified for being a "hall monitor" and the like.
the guy uses a newspaper column to support his argument for AFCIs .....whar "expert " would resort to that ?
You and others have tried to reason with the guy, and he just keeps on spewing out this garbage !
I've pulled large wire for VD, but current in a circuit doesn't change .......until this guy got his hands on it
In another case, you might need "50 amp" (or #6 )wire to overcome voltdrop on a long run and still be able to use all 20 amps. But I would still protect at 20 amps with a 20 amp socket at the end.
I don't see how that could possibly pass code. The recepticle is only rated at 20A. A couple of space heaters or heavy duty shop tools plugged in via a splitter would easily exceed that w/o tripping the breaker (I have a couple of space heaters which draw 12.5A each). This would cause the recepticle to overheat & potentially start a fire.
OTOH, while I don't know what the code book would say, putting a 20A recepticle on a 15A line wouldn't necessarily be a hazard since the breaker would trip if you exceeded 15A thus protecting the line & the outlet.
To me, it makes the most sense to match outlet ratings to line ratings.