NEC Changes For #14 Ampacity

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FionaZuppa said:
oh, i see what you mean. feed a step down xfrmer. where do you get a 12kW step down?
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Buck boost, or rewind a microwave oven transformer. In your case a 1 or 2kw unit will do. The 12kw unit is for circuit breaker testing which requires far more power.
 
mbrooke said:
Buck boost, or rewind a microwave oven transformer. In your case a 1 or 2kw unit will do. The 12kw unit is for circuit breaker testing which requires far more power.
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let me see what i can find.
 
FionaZuppa said:
yeah, ok, going the 20amp variac + MOT, a tad more work than i wanted to do with the MOT conversion, but this is the way fwd.
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Its the best way to do it imo. I know NRTL and other professional testing facilities use this approach. One reason I would avoid a step source like halogen bulbs is that even if you get the exact current you seek like 24 amps, as the wire heats up the current will go down a bit. Switching on another lamp may raise the current above your desired current draw. Further line voltage fluctuations can yield lower or higher numbers which the variac will ofset with a simple dial turn.
 
mbrooke said:
Its the best way to do it imo. I know NRTL and other professional testing facilities use this approach. One reason I would avoid a step source like halogen bulbs is that even if you get the exact current you seek like 24 amps, as the wire heats up the current will go down a bit. Switching on another lamp may raise the current above your desired current draw. Further line voltage fluctuations can yield lower or higher numbers which the variac will ofset with a simple dial turn.
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for this test, not so worried about the other factors to output control. but, the setup allows me other uses such as adjustable spot welding, so the extra cost and extra work is ok.
 
FionaZuppa said:
for this test, not so worried about the other factors to output control. but, the setup allows me other uses such as adjustable spot welding, so the extra cost and extra work is ok.
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IMO, something as small as 1 amp deviation can sway outcomes. Plus the bulbs have a limited life expectancy, not to mention 10kw of heat is enough to heat a small home in the dead of winter.


I know :lol: Im pushing the variac + MOT but its the only low cost method which gives the most bang for the buck.
 
mbrooke said:
I know :lol: Im pushing the variac + MOT but its the only low cost method which gives the most bang for the buck.
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well, i did mention i went with 20A vari + MOT a couple of posts back ;)

vari + mot = ~$140
ten 1k T3 halogens = ~$45

10kW worth of T3 halogens can be just as fun as vari/mot, but the vari/mot i can use elsewhere after this test.
 
FionaZuppa said:
well, i did mention i went with 20A vari + MOT a couple of posts back ;)

vari + mot = ~$140
ten 1k T3 halogens = ~$45

10kW worth of T3 halogens can be just as fun as vari/mot, but the vari/mot i can use elsewhere after this test.
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I know, just re-assuring you that you made the right move. :thumbsup:
 
and just an idea for you cable melters, a 12awg 22mH toroid air core makes it real easy to put #4 or #2 loops through, and the mag field is better from toroid = higher amps. 22mH on 120v 60Hz yields 14.4amps, but i would put a fan on it. paired to 20A variac its a good match. they are about $100US from UK maker.
 
FionaZuppa said:
which variables? output power into the wire?
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Id say so. Both line voltage and the NM heating will cause changes in current, so its important to keep the current constant. I will find a you tube video where the current actually dropped as the wire was heating.
 
mbrooke said:
Id say so. Both line voltage and the NM heating will cause changes in current, so its important to keep the current constant. I will find a you tube video where the current actually dropped as the wire was heating.
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as in real world scenario. thats why i suggested to wait for equilibrium and then go an extra 10min, take the readings, move dial up, repeat.
 
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