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Author Topic: Single Phase 240v to Three Phase 208v Cable  (Read 2082 times)

William Schnake

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Single Phase 240v to Three Phase 208v Cable
« on: March 12, 2016, 04:37:56 pm »

Let me start off by saying I only understand the basics of electricity and any actual work that is going to be done will be done by a friend of mine who is a licensed electrician.

My situation:
We have distros that are single phase 240 volt (2 hot legs/1 neutral/1 ground) and we have a distro which is three phase 208 v (3 hot legs/1 neutral/1 ground).

What I would like to do:
I just purchased a couple three phase Motion Lab Rac Pacs for my amp racks.  I would like to be able to use the Rac Pacs with either the single phase 240 volt distros or the three phase 208 volt distro.  The input to the Rac Pac is a Hubble HBL2815 30 Amp 30Y 120/208 VAC connector. The output from one of the single phase distros would be a NEMA L14-20 240/120 volt panel mount connector.

Based on the way the amp racks are setup my though was to do the following: Male L14-20 wired normally with 2 hots/neutral/ground Female HBL2815 30A wired as follows L1 + L3 tied together at the input cable end and L2 on it's own leg.  I realize this cuts down the amount of available power on L1 & L3.  However, the amps on these two combined legs don't draw as much as the amps on L2.  This is a specialty cable only to be use when we don't have Three Phase 208v available.

                      L14-20 240volt                          L1      N      G      L2
                                                                       |        |       |       |
                                                                       |        |       |       |
                                                                     /  \       |       |       |
                      Hubble HBL2815 208volt        L1    L3   N      G      L2

Last Thing:  We are using a 240volt 40 amp breaker at the L14-20 end.

Thanks in advance for your help and ideas.

Bill
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Geoff Doane

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Re: Single Phase 240v to Three Phase 208v Cable
« Reply #1 on: March 12, 2016, 06:20:47 pm »



Last Thing:  We are using a 240volt 40 amp breaker at the L14-20 end.



Your basic plan is sound, with the understanding that you may be somewhat limited on the total power draw.

But no licensed electrician should be putting a 40A breaker on the feed to an L14-20 receptacle.  If the L14-20 is already installed somewhere, it should already be on a 2-pole 20A breaker, and you don't need to add any overcurrent protection to the adapter.

Strictly speaking you also shouldn't try to put two wires into one lug in the connectors, either at the L14-20 or the 3-phase connector  (BTW, a 2815 seems to be an inlet flange, not the mating connector like you have the diagram drawn).  The L21-30 receptacle might have to go in a box where the connection can be made properly.  I'm also assuming you don't have anything in those racks that actually needs 3 different phases.

GTD
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William Schnake

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Re: Single Phase 240v to Three Phase 208v Cable
« Reply #2 on: March 12, 2016, 09:09:57 pm »

Your basic plan is sound, with the understanding that you may be somewhat limited on the total power draw.

But no licensed electrician should be putting a 40A breaker on the feed to an L14-20 receptacle.  If the L14-20 is already installed somewhere, it should already be on a 2-pole 20A breaker, and you don't need to add any overcurrent protection to the adapter.

Strictly speaking you also shouldn't try to put two wires into one lug in the connectors, either at the L14-20 or the 3-phase connector  (BTW, a 2815 seems to be an inlet flange, not the mating connector like you have the diagram drawn).  The L21-30 receptacle might have to go in a box where the connection can be made properly.  I'm also assuming you don't have anything in those racks that actually needs 3 different phases.

GTD

Geoff, thanks for responding.  You are absolutely correct that should have said L21-30 instead of the HBL2815.  The HBL2815 is the panel mount on the Motion Labs input. 

I can't explain why there are 240 volt 40 amp breakers on the L14-20s in the tap.  All I know is that's how I bought it and it has always been that way. 

Thanks again.

Bill
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Geoff Doane

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Re: Single Phase 240v to Three Phase 208v Cable
« Reply #3 on: March 13, 2016, 08:16:44 pm »


I can't explain why there are 240 volt 40 amp breakers on the L14-20s in the tap.  All I know is that's how I bought it and it has always been that way. 


Do you use L14-20s for any of your racks?  If not, I would replace the L14-20s with L21-30s, change the breaker to a double-pole 30A, use 10 ga. wire or larger, and connect L1 to L3 with a note on the front panel to indicate this.  That way you don't need any "special" power cables or adapters, it's safe, and you can use the same cabling everywhere, whether your main distro is 3-phase or single.  I'm pretty sure L21-30 and L14-20 receptacles fit in the same panel opening, but you'd want to confirm that before proceeding.

If you are using L14-20s for something else, maybe you should just modify one or two of the receptacles on each distro for the time being.  But the other breakers should be changed to 20A while you're at it.

GTD
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Re: Single Phase 240v to Three Phase 208v Cable
« Reply #3 on: March 13, 2016, 08:16:44 pm »


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