So you can use 120 volt lightbulbs and timers and primaries on control circuit transformers, and fan motors. and all kinds of other low power devices without (illegally) using the safety ground as a neutral, potentially making the chassis "live" - as has been done, unofficially, for decades - on both dryers and ranges.
It's a "safety" thing. They initially allowed the use of the safety ground as a neutral as a matter of expediency due to the high price of copper
I got used to having the neutral when I was designing lab carts with
240 V DC motors. It was very handy to have 120 V outlets out in the middle of the lab for various tasks. My last set of carts were 440V explosion proof in a classified area, so no outlets on those anyway.I continued the practice when I built my shop, had the electricians pull 4 wire for all my 240 V. circuits. But I haven't had the need since distances are short to plenty of 120 V outlets in the shop.
I will probably relocate nearer the coast in the near future. I may end up adding 120 V outlets to the welding cart if needed at the new place.
Pete Keillor
I was only a few feet away from another tech when he tried to measure an SCR trigger circuit floating on 120V with a grounded scope. When he flipped the power switch the entire probe exploded from the enormous current in the braid, sending him to the hospital. I was facing away and didn't see but I think his body shielded me from the fireball.
-jsw
Defective breaker?
Parts of the probe remained attached. He had connected the probe ground to the SCR cathode (hot line) so he could observe the optically isolated SCR gate trigger pulse without interference from the 120V sine wave it was riding on. It was a 240V power supply so both sides of the SCRs were Hot.
OK, politics, like belt+suspenders. Got it. I'm going to have to ask who plugs those things into dryer outlets, too, I'm afraid.
Break out your meter and find out. There are 3 pin twist lock 110V plugs. I have a few.
"Jim Wilkins" wrote in news:pecbif$4e0$ snipped-for-privacy@dont-email.me:
Actually, if the load on the two 120V legs of the 240/120 service is reasonably well balanced, the neutral cable can be substantially *smaller* than the two hots. For example, I just helped my son install a new service panel in his house, upgrading from 100A to 200A service, and he just passed his final electrical inspection last week -- with two 3/0 copper cables for the hots, and 1/0 copper for the neutral. It actually would have passed with the neutral as small as AWG 4, but I happened to have enough 1/0 on hand already, left over from a long-ago project, and neither one of us had any 4.
*subtract the currents
Correct.
Further example, in case it's unclear to anyone: 75A on one leg and 90A on the other leaves
15A on the neutral.
A welder I had used a 120 volt fan. 240 volt welder.
Adding works if the direction is considered. I would have written 'add algebraically' to an audience of engineers.
"Jim Wilkins" wrote in news:pen9fb$lvh$ snipped-for-privacy@dont-email.me:
And I would have understood what you meant. Best to assume, though, IMHO, that most of the people reading this discussion aren't engineers, and would be confused by the terminology.
Since one current is arriving, and the other leaving, at the same point, they perforce have opposite signs -- but electricians and laymen don't think that way. They see 70A current on one leg, minus 30A current on the other, equals 40A in the neutral. and don't really care about the fine points of Kirchoff's Current Law.
Agreed, as long as they stick to single phase. I didn't want to plant an incorrect idea in case they move on to three phase.
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