# 3 phase 120/208V with a grounded neutral question



## jprebb (May 19, 2018)

Gentlemen, I’m hoping you might be able to help me with a question regarding a 3 phase PDUs and its proper receptacle in a data center environment in Japan. 

The PDU we were given to work with has a L15-30 plug. Our power source is 3 phases of 120V and a grounded neutral. Ultimately, I want my C13 receptacles on the PDU to have 2 of the 3 phases of 120V, so 208V measured between the phases and 120V measured between any phase and neutral. Can I still use a L15-30 receptacle as long as the ground on the receptacle is tied to the neutral? 

Thanks in advance for the education.

JP


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## Bird dog (Oct 27, 2015)

Please fill out your profile.


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## varmit (Apr 19, 2009)

The short answer is NO. An L15-30 is a 250 volt, 3 phase, with ground device.
For 208/120 volt, 30 amp, with a neutral and ground, use an L21-30. 

As always, something that will work and what is correct is a different situation.


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## jprebb (May 19, 2018)

Bird dog said:


> Please fill out your profile.


Done!

JP


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## jprebb (May 19, 2018)

varmit said:


> The short answer is NO. An L15-30 is a 250 volt, 3 phase, with ground device.
> For 208/120 volt, 30 amp, with a neutral and ground, use an L21-30.
> 
> As always, something that will work and what is correct is a different situation.


The problem is I only have the 4 wires to work with. I do not have a dedicated ground. 

The L21-30 is a 5 wire plug correct? What I think I truly need is an L18-30 receptacle. And if I need to lop off the L15-30 plugs on the PDUs and replace them with L18-30 receptacles, so be it. 

So then the question becomes, if presented with 3 phases of 120 and a grounded neutral terminated in a L18-30 receptacle, can I replace the L15-30 plugs on my PDUs with L18-30 plugs?

Again, thanks for your replies.

JP


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## Bird dog (Oct 27, 2015)

Ask your Japanese counterparts what power supply systems they have, because, you may have to reconfigure the PDU & use Japanese plugs. And of course your Japanese customer would love that, because, it would be plug & play for them.


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## joebanana (Dec 21, 2010)

jprebb said:


> The problem is I only have the 4 wires to work with. I do not have a dedicated ground.
> 
> The L21-30 is a 5 wire plug correct? What I think I truly need is an L18-30 receptacle. And if I need to lop off the L15-30 plugs on the PDUs and replace them with L18-30 receptacles, so be it.
> 
> ...


L18-30's are 4 pole, 4 wire. You can replace them, but you void the UL listing


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## jprebb (May 19, 2018)

Bird dog said:


> Ask your Japanese counterparts what power supply systems they have, because, you may have to reconfigure the PDU & use Japanese plugs. And of course your Japanese customer would love that, because, it would be plug & play for them.


Well, that's why I'm here actually. The PDUs have a L15-30 plug and the customer is asking what kind of receptacle I need to make this work. I'm hesitant to tell them to give me L15-30 receptacles though because it's the wrong application. However both plugs would work rating-wise (the L15-30 is rated for 250V vs. 208V of the L18-30)

So what exactly is different between being wired into a dedicated ground vs. a grounded neutral?

Thanks,
JP


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## micromind (Aug 11, 2007)

If the loads downstream from the cord and plug are 208 and not 120, the L15-30 will work. 

If they are a mix of 120 and 208, you'll need the L21-30. 

The L15-30 has all 3 phases and a ground but no provision for any 120. The L21-30 has all 3 phases and a ground and also a neutral so you can use any combination of 120 and/or 208 loads. 

I don't know how it is in Japan but in the US, just about everything needs to have a ground.


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## varmit (Apr 19, 2009)

In your OP the reference to 120 volt adds some confusion. As stated in "microminds" post, if all of the loads are phase to phase then the L15-30 connectors will be fine- AS LONG AS YOU ARE USING A BONDING CONDUCTOR AND NOT A NEUTRAL.


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## Bird dog (Oct 27, 2015)

A PDU is basically a power strip & is a factory assembly. So, are you redesigning a power strip? Please post a picture & info on the PDU you received.


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## jprebb (May 19, 2018)

varmit said:


> In your OP the reference to 120 volt adds some confusion. As stated in "microminds" post, if all of the loads are phase to phase then the L15-30 connectors will be fine- AS LONG AS YOU ARE USING A BONDING CONDUCTOR AND NOT A NEUTRAL.


Sorry about the confusion. A picture is worth a 1000 words (I cut-n-pasted the L15-30).


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## jprebb (May 19, 2018)

varmit said:


> AS LONG AS YOU ARE USING A BONDING CONDUCTOR AND NOT A NEUTRAL.


Also, I'm not sure I understand what this means. Can you please break this down a bit?

Thanks,

JP


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## varmit (Apr 19, 2009)

A neutral would be a current carrying conductor for, in this case, 120 volt loads. A bonding conductor (ground wire) is used to bond different parts of the system together to avoid differences of electrical potential between system and equipment components.

If the "neutral" is used as a bonding conductor, anywhere downstream of the service, this can cause current to flow through metal enclosures and equipment parts. This could potentially create a shock hazard.


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## jprebb (May 19, 2018)

varmit said:


> A neutral would be a current carrying conductor for, in this case, 120 volt loads. A bonding conductor (ground wire) is used to bond different parts of the system together to avoid differences of electrical potential between system and equipment components.
> 
> If the "neutral" is used as a bonding conductor, anywhere downstream of the service, this can cause current to flow through metal enclosures and equipment parts. This could potentially create a shock hazard.


Thank you for the explanation.

JP


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## LeboElectric (Apr 9, 2018)

Interesting


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## jprebb (May 19, 2018)

Quick update...customer's electricians say they can add dedicated ground, so we're going to go with a PDU that has the L21-30 plug. 

Thanks to all who replied.

JP


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