Color Coding Knock-down!!

Ok, it was'nt with my brother this time. The guyes at work and I, are having a dispute. On a Motor contactor (with overload), what color should the wire be that goes from the A2 terminal to the #95 terminal of the overload. I put red (115V) on the A1, 13, 14, and 95 terminals. The wire between #96 to the Neutral bus I put white. The say it should be red from #14 on the NO contactor to the #95 terminal of the overload. WHO IS RIGHT?
Thanks - - Barry.

NEMA factory built starters have this wire colored red.

If I was building a starter out of separate components then I would put the OL contact on the A1 side of the coil and connect A2 to the grounded conductor.

I agree Jim. I was under the belief that the only conductor that should be colored white would be from the last "Device" directly to the grounded conductor (Neutral Bus).

I also agree that the overload should be prior to the motor contactor, coil, and NO contact, although I have never seen the schematics written like this on the boxes that I have built.
Barry

Only that wire that is "fixed" to ground should be colored WHITE.

If there is a contact of some sort between a load of any kind and Ground, then the wire between the load and that contact should be RED.

WHITE is an extension of DIRECT GROUND!

Since you are talking about A2 terminal and #95-96 terminals, I assume you are talking about an IEC contactor instead of a NEMA contactor.

I concur Jim and Barry. Place the OL contactor on the control side of the contactor. Neutral switching the coil through the OL is the old way of doing things and is becoming less commonly used. I don't think I have ever seen it used that way on an IEC print.

The OL contact after the coil is an old NEMA standard (but not a requirement). The placement after a coil made it easier for a single OL contact to control multi-coil devices (like reversing starters). The aruguement for this placement was: the wires are short and factory installed "internal" to the contactors so damage is very unlikely.

Alaric, Jim etc are correct, the old way switched the neutral on the overload. This is no longer the correct method even by US standards. This is how it "was" done:


The new standard is as mentioned, place the OL on the powered side of the contactor. I will provide pictures for that if wanted but having a problem doing it right now. NOTE the above picture does not show a control transformer or power supply being used, this is technically incorrect by todays standards.

Is it against NEC code to wire the "old" way? This old way is common in our plant and makes it easy to interock all motors so if one trips out all motors drop out.

glenncovington said:

Is it against NEC code to wire the "old" way? This old way is common in our plant and makes it easy to interock all motors so if one trips out all motors drop out.

Click to expand...

It is not against code.

NFPA 79 (2002 Edition) deals specifically with this.
Section 8.3 says:
"Control Circuits shall be permitted to be grounded or ungrounded. Where grounding is provided, that side of the circuit common to the coils shall be grounded at the control transformer" ...
"Exception No. 2: Overload relay contacts shall be permitted to be connected between the coil and the grounded conductor where the conductors between such contacts and coils of magnetic devices do not extend beyond the control enclosure"

glenncovington said:

Is it against NEC code to wire the "old" way? This old way is common in our plant and makes it easy to interock all motors so if one trips out all motors drop out.

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No, its not a code violation. If you were to buy a NEMA reversing starter off the shelf today, it will most likely still be wired with the OL contact after the coils.

What you do really depends upon your needs. With the trend to move all control functions, even basic motor start/stop to the PLC, the trade practice is swinging towards placing the OL NC contacts in series on the control side of the coil and the NO contacts to a PLC input.

One thing you do not want to do is wire the NO and NC contacts of same contactor to wires of a different polarity or power source.

Consider the following situation:


The OL contact is wired after the starter coil, but the OL also has a NO contact that is wired back to a PLC input so that an overload alarm might be annunciated. All is OK until the OL trips. The bottom sketch shows what can conceivably happen while the contactor traverses the gap if the contactor does not travel uniformly away from the lower contacts to the upper contacts. Its obvious that this is not a good situation. If however the OL contact is on the control side of the coil this does not present a problem (as long as the voltages are the same, but then you should never mix voltages on the NO/NC side of the same contact anyways.

Some IEC OLs are made so that the NC and NO contactors are isolated from each other - but I wouldn't just automatically assume that all contactor OLs are made that way. Many manufacturers make good quality components, but as we all know, there is a plenty of junk out there as well. Its the junk that causes the concerns.

I think that is the primary reasoning driving the trend towards placing the contact on the control side of the coil.

rsdoran said:

Alaric, Jim etc are correct, the old way switched the neutral on the overload. This is no longer the correct method even by US standards. This is how it "was" done:

The new standard is as mentioned, place the OL on the powered side of the contactor. I will provide pictures for that if wanted but having a problem doing it right now. NOTE the above picture does not show a control transformer or power supply being used, this is technically incorrect by todays standards.

Click to expand...

Ron you stated in:

http://www.plctalk.net/qanda/showthread.php?t=14006

about this same picture

rsdoran said:

If you noticed the first picture used a DC power supply for the control circuit, either a 120vac or 24vdc supply is standard especially when a plc is involved.

Also note that the picture above is in no way improper or incorrect. To this day many systems are wired direct with supply voltage. I also dont care for this method but it is acceptable.

Click to expand...

So I'm confused, do you say it is correct or incorrect? Please don't take this as trying to start an argument, I'm just trying to figure out which is the correct way of doing this and I do respect (and learn from) what you say.

Bruce

The picture represents what "WAS" common at one time, thats why they sell 480vac (and higher) coils for starters...it is still done that way in some situations, like a remote pump station...

I am looking thru Article 430 of the NEC Handbook and it mentions the use of transformers to reduce the control voltage but I have not seen where it is required.

The main thing is safety, it can be dangerous when a motor starter uses 480vac for control. One time at work a maintenance guy pushed a button to start a vacuum pump and it went BOOM and the door flew off and hit him. I hit my head when I jumped and gashed it open, I ended up more hurt then he did and I was not working in the same area.

Technically the above can be done but whether it is "correct" would depend on the situation. I wont do it that way if I can help it.

WoW. Where else can a guy go to get- 1) the straight answer, 2) the "experienced" opinons of those who are in the field, 3) references to current (and old) code, 4) illustrations of the event, and 5) and education that is not tainted with embarresment for even asking the question.........
Thanks!
barry