bky
Gold Member
OK I hate to get on a soap box. I hear this statement all the time. (it bothers the heck out of me) current kills weather it's 220 or 110 volts.
sorry i cant help it.
Adding 220v welding circuit to the shop/garage
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OK I hate to get on a soap box. I hear this statement all the time. (it bothers the heck out of me) current kills weather it's 220 or 110 volts.
sorry i cant help it.
tshep
Gold Member
grs - you memorized a good rule, just not all of it!
310.16 *'s take you to 240.4 D, which basically says general purpose (non-exception) circuits are as you know.
BUT special circuits can be otherwise - 240.4 E through G.
For instance, I do heat pumps that call for smaller wires on bigger breakers - say #14 on a 20 or 25. Seems to be against the rules.
But, the idea is that UL has tested the failure modes for certain devices and they are such that the conductor will not fail with that size breaker protecting the circuit for startup time, for instance. If it is locked up, it's a short enough time yet such a big overload rate that the breaker will still trip long before the wire gets hot. The difference between load and overload is inherently greater than just one too many toasters!
The supply breaker, the conductor, and the specific load are all part of the system. Different loads act in different ways - and may have exceptions.
Another thought, for all, is not to just look at conductor cost if you are the one paying the electric bill. If there is some real chance you may actually spend some real amount of time paying to flow near max amps of electricity through that minimum size conductor - buy a bigger conductor made of copper, or you are just paying to heat up dirt, or your garage or worse - and maybe then paying again to aircondition that heat back out. All those ohms that make that conductor voltage drop multiply out to watts that convert directly to BTU's of heat. I can garantee you tommorow's electricty is gonna' cost more than today's copper!
Most electricians get into bidding habits, and then miss opportunities to save operating costs in their own systems.
310.16 *'s take you to 240.4 D, which basically says general purpose (non-exception) circuits are as you know.
BUT special circuits can be otherwise - 240.4 E through G.
For instance, I do heat pumps that call for smaller wires on bigger breakers - say #14 on a 20 or 25. Seems to be against the rules.
But, the idea is that UL has tested the failure modes for certain devices and they are such that the conductor will not fail with that size breaker protecting the circuit for startup time, for instance. If it is locked up, it's a short enough time yet such a big overload rate that the breaker will still trip long before the wire gets hot. The difference between load and overload is inherently greater than just one too many toasters!
The supply breaker, the conductor, and the specific load are all part of the system. Different loads act in different ways - and may have exceptions.
Another thought, for all, is not to just look at conductor cost if you are the one paying the electric bill. If there is some real chance you may actually spend some real amount of time paying to flow near max amps of electricity through that minimum size conductor - buy a bigger conductor made of copper, or you are just paying to heat up dirt, or your garage or worse - and maybe then paying again to aircondition that heat back out. All those ohms that make that conductor voltage drop multiply out to watts that convert directly to BTU's of heat. I can garantee you tommorow's electricty is gonna' cost more than today's copper!
Most electricians get into bidding habits, and then miss opportunities to save operating costs in their own systems.
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dstig1
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Note I said 20 a PLUGS are rare, not receptacles. I have only seen 2 things in my life with a 20A/120V plug on it, and one was a high powered industrial heat gun. I've seen plenty of 20A/220V plugs, and plenty of 20A/120V Receptacles...
I am unfamiliar with the TR outlets you are referring to. Something new in the code???
ssmith general
Bronze Member
OK I hate to get on a soap box. I hear this statement all the time. (it bothers the heck out of me) current kills weather it's 220 or 110 volts.
sorry i cant help it.
It's the amps that kill.
not2old
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My small mig welder is a Miller that has an input of 20amps, 120 volts with a 15 amp plug from the factory. I've occasionally used it on a 15 amp circuit until the breaker trips repeatedly. Awhile after I plug it into a different circuit, the welder's internal breaker will trip before the next panel breaker trips. I'm told this shouldn't happen, but it has done so at several different places I've used the welder. Breakers and wire must both heat up, wether or not the load is at the maximum or not.
grsthegreat
Super Star Member
TR receptacles are tamper resistant receptacles. they were new last code revision (2008). They suck, and i get nothing but complaints from homeowners about them.
they have a little trap door behind both openings that will not allow anything to be inserted into it unless something is inserted into both openings at the same time. and the black receptacles with the white TR doors (since all TR receptacles use the white colored interior covers) are not very attractive.
also, i realize that current kill, but Ive been shocked with 110, but Ive been thrown for a loop with 220. If there going to pass a law requiring TR receptacles for 110, it should also be passed for 220. thats all I'm saying. there are too many ambiguities in the code.
dstig1
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Oh goody. Sounds like something that gets swapped out the moment the inspector signs off... I haven't heard about them around here, but we may not be on NEC2008 here yet. I need to check into that...
Edit - just checked and they adopted 2008 in early '09. Ah well...
Edit - just checked and they adopted 2008 in early '09. Ah well...
Inspector507
Super Member
Actually if you use 90C wire it could possibly go as high as 80A. 200% of 40A is 80. But I wouldn't do it.
If you look at the text of NEC 240.3 it says:
240.3 Other Articles. Equipment shall be protected against overcurrent in accordance with the article in this Code that covers the type of equipment specified in Table 240.3. Copyright NFPA
Then look at Table 240.3. Under Welders or Electric welders I forget which it directs you to Article 630. That is out of the 2008 NEC, not 2011. We don't enforce that yet until maybe Jan 2012.
edit.........just checked the 2011 NEC. It's still the same.
grsthegreat
Super Star Member
the only thing i know for sure anymopre....is the inspectors only allow us to use the 60 centigrade tables anymore for our load calcs..been that way here for about 6 years (2 code cycles)
Inspector507
Super Member
As you can see, there are more ways to apply ampacity limits than just 310.16. Just depends on your application. On 100A or less you use the 60C column. On over 100A you use the 75C column. For derating you use the 90C column if you have 90C rated conductors.
Well......
Unless all your terminals are rated higher
Unless it's a wet location
Unless it's in thermal insulation
Unless..........
There are so many exceptions in the NEC it's mind boggling.