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Old 07-25-2019, 08:46 PM   #1
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Default Three Phase Motor Plugging(Forward/Reverse)

Hello first post here. I have been doing controls for the last 10 years and have ran across a first for me. A company built a drill/tap machine that as I now know uses plugging, reversing a motor while it is still running forward. The motor is a 3hp motor using old Allen Bradley nema 705 Bulletin forward reversing contactors. These are now obsolete and have been replaced with the 505 series.

My question is, Has anyone ever replaced these NEMA contactors with IEC forward/reversing? Specifically in a plugging application this seems like murder on a contactor. I know the NEMA style contactors are tanks but they come with the price tag. The AB spec sheets list them as capable but I'm more looking for some real world experiences.

Thoughts, opinions?

Thanks.
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Old 07-25-2019, 09:06 PM   #2
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Originally Posted by IASMICHIGAN View Post
Hello first post here. I have been doing controls for the last 10 years and have ran across a first for me. A company built a drill/tap machine that as I now know uses plugging, reversing a motor while it is still running forward. The motor is a 3hp motor using old Allen Bradley nema 705 Bulletin forward reversing contactors. These are now obsolete and have been replaced with the 505 series.

My question is, Has anyone ever replaced these NEMA contactors with IEC forward/reversing? Specifically in a plugging application this seems like murder on a contactor. I know the NEMA style contactors are tanks but they come with the price tag. The AB spec sheets list them as capable but I'm more looking for some real world experiences.

Thoughts, opinions?

Thanks.

I have done quite few of them and with IEC contractors you will need to be oversized at least twice of normal rating so like example a 16 amp unit may be ok for non plugging duty but once you get into plugging duty you will have to oversized to 32 amp verison to handle the inrush current during plugging mode.,

I just hope you are aware you will need a super short off delay when you hit plugging mode.

read the fine print note on 505 series units about derating on plugging duty that will get your attention.
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Old 07-25-2019, 09:33 PM   #3
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Why do you need to replace the 705’s for? As far as I know all wear parts are still available from AB. @Cow has a source he gets reman starters from, Oregon Breaker I believe. My usual source is eBay of course. I believe a company called Hoyt sells aftermarket parts also. Think twice before you toss those old AB’s and install any brand of IEC.
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Old 07-25-2019, 09:56 PM   #4
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Plugging is an EXTREME measure that if done repeatedly will destroy a motor.

The only situation where I'd use plugging in an engineered scheme is Life Safety.

In all other situations -- the common brake is to be spec'd.

That approach is as common as dust.

Plugging stresses the windings to a crazy degree.

BTW, plugging does not stop the motor -- it reverses it.

Going backwards is not at all the same as stopping the motor.

Last edited by telsa; 07-25-2019 at 09:59 PM.
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Old 07-25-2019, 10:15 PM   #5
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I have done quite few of them and with IEC contractors you will need to be oversized at least twice of normal rating so like example a 16 amp unit may be ok for non plugging duty but once you get into plugging duty you will have to oversized to 32 amp verison to handle the inrush current during plugging mode.,

I just hope you are aware you will need a super short off delay when you hit plugging mode.

read the fine print note on 505 series units about derating on plugging duty that will get your attention.
I agree, if you're using IEC stuff, go WAY oversize.

Allen Bradleys specs for a NEMA size 0 contractor (any of the 500 series) is 5HP @ 460 volts for normal duty and 2 HP for jogging/plugging. The size 1 is 10 HP for normal and 5 HP for jog/plug.
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Old 07-25-2019, 10:22 PM   #6
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Originally Posted by 460 Delta View Post
Why do you need to replace the 705’s for? As far as I know all wear parts are still available from AB. @Cow has a source he gets reman starters from, Oregon Breaker I believe. My usual source is eBay of course. I believe a company called Hoyt sells aftermarket parts also. Think twice before you toss those old AB’s and install any brand of IEC.
@frenchelectrican Good to know thanks!

@delta This is on AB technote 824309. "Repair part support for the Bulletin 705 Reversing Starters - Series A, B, C design ended on 31-December-1993."

I've seen some aftermarket repair kits but have had trouble finding documentation showing the allen bradley part numbers and it doesn't seem my local distributor carries them.
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Old 07-25-2019, 10:31 PM   #7
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Plugging is an EXTREME measure that if done repeatedly will destroy a motor.

The only situation where I'd use plugging in an engineered scheme is Life Safety.

In all other situations -- the common brake is to be spec'd.

That approach is as common as dust.

Plugging stresses the windings to a crazy degree.

BTW, plugging does not stop the motor -- it reverses it.

Going backwards is not at all the same as stopping the motor.
I would agree but these motors on this machine are still plugging away lol (couldn't resist the pun). They cycle For/Rev every 20 seconds and the machine is relay logic from the early 80s.
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Old 07-25-2019, 10:32 PM   #8
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What about switching to a vfd and using the dynamic brake mode? (I think that is the right function)
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Old 07-25-2019, 11:43 PM   #9
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Welcome aboard @IASMICHIGAN!

+1 for French's comment on severe oversizing.
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Old 07-26-2019, 08:22 AM   #10
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To the OP: has your customer heard of TapMatic?

TapMatics can be purchased off of eBay for peanuts.
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Old 07-26-2019, 07:38 PM   #11
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Plugging is indeed hard on motors, but typically it is dealt with by over sizing the motor in order to get mechanical components larger and stronger than typically used on the HP size you need. So if it has been working for years, that is likely the case, i.e. the machine needed 1HP, they used a 3HP motor.


If you use IEC contactors, you should use the AC-4 duty ratings, then I always go up one more size from that, because the IEC concept of plugging as denoted in AC-4 is not the same as the NEMA concept of plugging. Do NOT relay solely on the electrical interlocks, get a mechanical interlock for the contactors as well.
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Old 07-27-2019, 05:25 AM   #12
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Yes, plugging motors is very common on older bag fillers that are controlled by weight. Instead of stopping the motor, it is reversed for about 2 seconds to prevent overfilling the bag. It is a brutal application, but with a NEMA starter and a properly sized motor, these things seem to last forever. The key element is to have a short delay, about 1 second, between forward and reverse.

If you can have an "almost full" sensor, to ramp down a VFD, it works really well.
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Old 07-27-2019, 09:57 AM   #13
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Quote:
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To the OP: has your customer heard of TapMatic?

TapMatics can be purchased off of eBay for peanuts.
Hmm those are interesting. I have not seen those, but I will look into them.
@JRaef I would agree with interlocking. I always electrically and mechanically interlock for piece of mind. I’ve seen just mechanically interlocked contactors get welded shut.
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Old 08-03-2019, 01:49 PM   #14
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Cycling every 20 seconds is harsh enough without the plugging aspect. Personally I would try very hard to talk a customer out of any IEC components, even going as far as to say I wouldn’t be responsible for their eventual demise.

If I was in your situation I’d contact the manufacturer and see what they are using these days. They may even have a recommendation on replaceable but obsolete parts.


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