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Old 03-08-2019, 08:05 PM   #1
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Default Motor Circuit Question

Cant find anything in the codebook about this. Is it within code to have a recipticle and plug between the motor starter and the motor? Does this seem practical? Would be using something like the hubbell 480v 50amp twist lock. Recipticle would be mounted on a junction box fed by the motor starter with the motor plugged into it.
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Old 03-08-2019, 09:36 PM   #2
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It's done all the time.

http://www.meltric.com/

I would NOT be using a twist-lock for 480 motor loads.

Strictly Pin & Sleeve for me -- and Meltric -- which, technically, is not P&S.

In the real world, such connections get tough abuse.

That's the whole reason that pin & sleeve designs were ever crafted.

The Meltric system is designed for ultra-quick change outs.
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Old 03-08-2019, 10:13 PM   #3
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I've done this a number of times.

In my experience, using basic twist locks is ok for small motors. I think just about every TL I've seen has a HP rating.
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Old 03-09-2019, 12:09 AM   #4
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When you use a standard twist-lock, you have to use it at the HP rating it has (if there is no HP rating, you can't use it) and that HP rating will be less than the amp rating might otherwise allow. For example an L16-20 is rated 20A, but only 10HP at 460V, which is 14A. That's because of motor inrush and if someone uncouples it without turning it off, it will flash over. So they are also supposed to be used only when the power is already disconnected, even at the reduced ratings. For that reason you can buy them with a disconnect switch built-in, which also gives you the LO/TO point.



The original pin and sleeve devices were called "arc tight" for that reason, they contain the arc inside of the guard so that nobody gets hurt. But technically they too are supposed to be disconnected first, so for motor loads you are supposed to use the versions that are mechanically tied to a disconnect device as well.


The Meltric take it one step further and actually have a disconnect switch rating all by themselves. The pins are spring loaded so that when you begin to uncouple them, the contacts open inside, like a mechanical contactor, and disconnect power before the pins and sleeve separate. Meltric were for a long time the only ones rated to not need another disconnect device, but others have come out with competitive versions now (Hubbell for sure, maybe others).
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Old 03-10-2019, 12:26 PM   #5
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I've noticed smaller of our smaller machines (10hp or smaller motors) have a twist lock cord and plug comming out of the control panel ( feeds the motor starter and control transformer) and plugging into a recipticle. I don't see a hp rating on the hubbell 50amp twist lock plug that being used in most cases. These need to instead be something like the Meltric or a pin and sleeve type?
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Old 03-10-2019, 01:14 PM   #6
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Get the Hubbell connector number and click over to their website for all of the specs.

All recent Hubbell twist-locks carry some horse-power rating. (AFAIK)

Don't be surprised if the device is under-sized -- not appropriate for the motor's draw.
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Old 03-10-2019, 01:26 PM   #7
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I been using the Meltric pin and sleeve type pretty often and they have very specific ordination so you cant jam a wrong one at all.

JRaef did posted a very good answer on this one and he covered it well.


Yes the Hubbel and other brands twistlocker will have HP rating on them but not always so double check to make sure they are rated for X size of motor.
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Old 03-10-2019, 02:16 PM   #8
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Plug- HBL7765C

https://www.hubbell.com/hubbell/en/P...detail-section

Recipticle- HBL7379

https://www.hubbell.com/hubbell/en/P...L7379/p/176126


This is the plug and recipticle we mainly use. Don't see a hp rating anywhere on any of the documents.
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Old 03-10-2019, 02:36 PM   #9
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The one Meltric I installed seemed well made and suited for the use intended. This was for a irrigation pump removed every year at the end of the season. Having the disconnect right on it is great.
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Old 03-10-2019, 04:01 PM   #10
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Quote:
Originally Posted by Maintenance2 View Post
Plug- HBL7765C

https://www.hubbell.com/hubbell/en/P...detail-section

Recipticle- HBL7379

https://www.hubbell.com/hubbell/en/P...L7379/p/176126


This is the plug and recipticle we mainly use. Don't see a hp rating anywhere on any of the documents.
I am famuair with that one .,,

No it do not have HP rating at all just voltage / amp rating only techally it can handle 5 HP motor ( @ 230V 3 PH ) without issue but I will not use this for motor purpose.,

I would go with pin and sleeve style it much better useage for this purpose.
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Old 03-11-2019, 01:02 AM   #11
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Does the recipticle still need to be rated for the hp of the motor if it is fed by a disconnect and power is it be shut off before motor is unplugged? Is this rating for only if the recipticle is to be used as a disconnecting means or is this rating for normal operating conditions?
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Old 03-11-2019, 01:10 AM   #12
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Is the hp rating on recipticles for normal condition? Or is it a load break hp rating? Meaning the largest hp motor you can break with the plug
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Old 03-11-2019, 01:38 AM   #13
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The 'budget' is NOT your problem.

The performance of installed equipment can be held against you -- for your expertise.

The cost of electrical gear is trivial compared to the associated power bill -- if you're talking industry.

Don't buy into the management's budget tears.

Why the conservative design?

Have you ever taken a gander at the payouts for injuries?

Don't design to Third World 'standards.'

Last edited by telsa; 03-11-2019 at 01:43 AM.
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