Electrical question on connection - L15-30 VS L14-30

[Bad Bubba]

Having my electrician come over to put in a subpanel with a GFCI 30 Amp breaker in it. He has specified a cord with an L15-30 receptacle. I have questioned him about it but he insists that is the correct plug for my needs. It seems to me an L14-30 is the better choice, but I am not the electrician. Any thoughts

 

[Brumateur]

NEMA L14 are three-pole and ground connectors rated for 125/250 V. Intended for three-pole, four-wire hot-hot-neutral-ground circuits .
NEMA L15 are three-pole and ground connectors rated for 250 V. Intended for three-phase circuits.

Are you installing subpanel at your home (L14 )or at some shop with 3phase wiring (L15) ?

 

[Bad Bubba]

Single Phase at home. That is what I thought. I am an engineer but not an EE.

 

[Brumateur]

So you need an L14-30R

 

[duncan.brown]

Seconded. If it’s a domestic supply, you have two hot taps of a center-tapped transformer that give you single phase 120v to the neutral center tap and 240v across the two hot taps. You want the two hot wires, neutral, and ground, so L14-30 the right outlet for single phase domestic supply.

if you have a three phase supply in your house needing an L15-30, then I would be... uh... shocked.

 

[Bad Bubba]

Funny story follow up - I check with the electrical company and the guy who wrote the quote insisted he had the correct plug. Due to my own concerns, went out the night before and purchased an L14-30 plug to have on hand. The crew showed up and installed the panel and when they went to add the plug the electrician (not the guy who did the quote) came to me to tell me we had a problem because the plug was not right and he would have to see if they had one in stock back at the shop. I whipped out the plug I had purchased and the guy was elated - told me what an awesome client I was. They finished the job up and took the charge from the plug and the trip charge off the invoice.

These guys have done several projects for me over the years and have always been great - I think they are over whelmed. They told me their workload was way up during the pandemic.

 

[RancherGuy]

To answer the question of L14-30 vs L15-30, I have confirmed the difference. I have two different projects going, so I ordered both in both P(lug) and R(eceptacle)/C(onnector) varieties.

They look exactly the same but the purpose is different, so the wiring is different - one is for 240V single phase, the other is 240V 3 phase. The bent blade is Ground for both. For the remaining 3 blades, either 2 are hot or 3 are hot.

My orders were not arriving in the order that I could use for implementation, so I decided it didn't matter if I used L14 for L15 or vice version, since in my hand they all looked identical. Where I should have used L14, I wired up an L15 Connector (receptacle plug). Did a great job by the way, and double-checked the wiring. When I tried an L14-30P, I found 3 blades fit but not the fourth. This is a good thing. It means that when used correctly I cannot plug a single phase device into a 3 phase outlet and fry my equipment or create a fire or health hazard.

So here is the detail on the L15 Pass & Seymour Connector that I used. Know how regular household outlets and plugs have one blade wider than the other? Same goes for L14 vs L15. One of the L14 hot blades is wider than L15. Maybe there is not as much danger trying the inverse of what I did - to plug 3 phase into single phase, because the device would only get 2 hots instead of the necessary 3 hots. But do not contemplate grinding the wider L14 blade so it fits into L15 - thats could create a very dangerous result down the line.