Why are motors not current limited?

[rbowman]

Either one...

[Clare Snyder]

Fromwhat I remember, Canadian code required separation of the circuits UNLESS the fuses were "ganged".

In MOST cases the circuits could be easily separated, not having 2 lseparate live feeds in a single box. In situations where that was not possible or feasible, the "ganged" fuses were required. In actual real-world situations, it was not common to run into the situation.

My house had a "stove block" a "drier block" plus 4 ganged fuse pullouts - 2 for kitchen outlets, one for the AC and one for another "edison circuit" The fuse and drier blocks had cartridge fuses - the rest were plug fuses.

Back in the 1969 code book - section 12-296 is states "conductors of different systems shall not be installed in the same box,, cabinet, or auxilliary gutter unless:

1 a barier of sheet steel not less than 0.0528 inch (16msg) or ane equivalent device of acceptable insulation material is used to devide the space into separate compartments for the conductors of each system

- - - - - . Therer are exceptions listed

Also, in14-032 In branch circuits derived from a 3 wire grounded neutral systen (Edison circuit) 2 single pole manually operable circuit breakers may be used in lieu of a 2 pole breaker, providing that:

1) their handles are so interlocked that all ungrounded conductors will be opened by the manual operation of either handle; AND 2) each breaker has voltage ratings not less than that of the 3 wire grounded system

So the linked breaker was required by (at least Canadian) code as early as 1969 for Edison circuits, and separate "systems" (read that as circuits) were not allowed in the same box.. I could look it up in

1966 code too if I could find my book. My '69 book was close at hand.

[trader_4]

I would take that to mean "different systems", eg low voltage signaling in the same box as 120V plus. Not different circuits of the same system. That is where they specify a divider if you're using the same box. An Edison circuit is actually the same branch circuit, at least I'd consider it to be one circuit.

[gfretwell]

"Different systems" does not apply, that refers to separately derived systems or services with different voltage characteristics. I am not quite sure how they could have specified "breakers" in 1969 since fuses were still pretty popular. The NEC had no such requirement. I agree if breakers were present, you might make that stick but multiwire circuits predate the first breakers by decades.

[Clare Snyder]

They also pre-date "standards"

[gfretwell]

The first version of the NEC came out in 1898 in New York City.

[Clare Snyder]

And I own a copy of the "american electrician's handbook" by terrell Croft first printed in 1913 and reprinted in 2014 by McGraw-Hill Book Co in New Yoirk - passed down through the family

[Jimmy Wilkinson Knife]

No it isn't. It won't exceed 20 amps. But it might not be zero.

Why do they use 480?

[gfretwell]

Same reason you are pimping for 220. It allows smaller conductors for a given amount of delivered power. 480 is common for services to large installations like office buildings and gets distributed to each floor as 480 where a transformer will take that down to 120/240 or 120/208. The house lighting will usually be 277 using one 480v phase to neutral.

[Ralph Mowery]

Most places that have equipment that uses lots of power in the US will have 480 volt 3 phase equipment such as motors. The lights are most often 277 volts single phase as that is the neutral to one hot leg of the 480 volt 3 phase circuit.

Really big users will have even higher voltages. The plant I worked for had a power room where the power from the electric company was converted from whatever they sent us to 13,200 volts. This was sent to other parts of the plant where it was mostly conveted to 480 V 3 P. There was some equipment that used around 4,000 volts. I did not usually work with that and don't recall the exect voltage, want to say 4100 volts.

Then we got is some junk from Europe that used 380 V 3 phase. They even reversed the safety color code on the main disconnects. To the US it was green for power on, and red for power off. Their junk was green -- power off--safe to open the door to the electrical box. Red was power on-- not safe to open the door.

Once the color code for danger (off/on) is changed there might as well not be one. Probably safer if not used.

[Jimmy Wilkinson Knife]

As late as 5 years ago Nvidea graphics cards could overheat and destroy themselves. AMD ones don't though. Not tried a more recent Nvidea as AMD are better value for money.

I've yet to see a car which does this (certainly not with overheating, I've not had anything else life-threatening for an engine on recent cars).

[rbowman]

We leased an old bakery where the freight elevator was 550. After 40 years of home repairs the 550 showed up in the damnedest places. I never made any assumptions about what I'd find when I opened a panel.

[gfretwell]

The strangest panel for the uninitiated is 3 p corner grounded delta. It will look exactly like single phase 120/240 (2 pole breakers, 2 hots and a white grounded conductor) except there will be 240 to ground and you will have 240v 3 phase equipment hanging off of it. The first time I saw it I took a minute to figure out what I was looking at. The only place you will see it is where there are pretty much all 3 phase loads and maybe some 240v L/L load.

[Ralph Mowery]

That sounds right to me. We had all kinds of voltages in that plant and I never did memorize some of them as I seldom worked on them.

Mainly worked daily with the 480, 120 aC, and some low voltage 24 volt/20 ma DC instrument loops. It really was important to pay attention as to what wires you were on as sometimes all that and some thermocouple wires could all be in the same cabinet inches apart.

Then I came across a couple of 208/120 Volt 3 phase type circuits.

[Clare Snyder]

The Limeys "open" a switch to turn something on too - and "close" it so shut something off - - - -

In Canada installing the equipment with the switches mislabelled that way would be illegal - it would not get the "special inspection" tag without correction and would most definitely not get a VALID UL or CSA tag.

[Clare Snyder]

600 volt 3 phase delta (no neutral) is also pretty common.

[Clare Snyder]

Also the old "wild leg delta" where one phase is center tapped to give a standard single phase service for "office" use while providing

208 3 phase for "shop" loads.

AKA 3 phase 4 wire delta. Not common any more but was VERY common years ago. Only 2 of the phase to neutral connections could be used because the third "wild" or "high" leg was somewhere around 208.

[gfretwell]

Center tapped Delta is far from unusual here. It has the advantage of supplying the full 240v on the line to line loads instead of 208. You just look for 2 transformers on a pole and one usually larger than the other.

The larger one supplies the 120/240 load.

[Clare Snyder]

Still common here on "existing" installs. but rather uncommon on new builds = around here.

More common to hav e "lighting" or "pffice" transformer running off one phase with primnary voltage to match the 3 phase, with center tapped 240 secondary for the 120/240 loads.

[Jimmy Wilkinson Knife]

I never said they overload the neutral, I just refuted that there would be ZERO neutral current with two loads plugged in.