L14 to L5 Y-Cable

[albinotuba]

Hi All,

I came across an odd Y cable in our stocks; it has an L14-30P on one end and 2x L5-30R on the other. What's interesting is that the 2 L5-30 connectors are wired to different hots on the L14, and the neutrals are bonded together (as are the grounds), making the two hots out of phase.

Is it safe to use this cable? Is there any risk of overloading the neutral? What is the maximum safe load that can be drawn using this cable? Is it safe to draw 30Amps from both L5-30s simultaneously?

Thanks!

 

[Footer]

Perfectly legal. Your connectors are matched. If it was made with properly gauged wire and terminated correctly you are fine. There is no difference between this and the very common L14-20 doghouse.


The only issue with it is that the breaker will be bonded at the distro... so if you overload one leg you lose both.... but that is an issue with any multi-phase power drop.

 

[derekleffew]

Perfectly legal. ...

Perfectly? Is the apparatus in question Y-style or V-style in construction? If the latter, is the L14-30P listed, by NRTL for use with TWO cable entrances? Two conductors in the W and G terminals?

Note that while a male L14-30 to two female L5-30 may (and I'm not saying it is) be acceptable, the opposite: one-female-to-two-males most certainly IS NOT.

 

[Footer]

Perfectly? Is the apparatus in question Y-style or V-style in construction? If the latter, is the L14-30P listed, by NRTL for use with TWO cable entrances? Two conductors in the W and G terminals?

Note that while a male L14-30 to two female L5-30 may (and I'm not saying it is) be acceptable, the opposite: one-female-to-two-males most certainly IS NOT.

Hence the "terminated correctly" part. Just because you can shove two conductors under a lug does not mean you should...

 

[albinotuba]

Perfectly? Is the apparatus in question Y-style or V-style in construction?

Y-Style. Assuming the cable is properly constructed and terminated, is there any risk of overloading the neutral? What about maximum current draw? Assuming the wires are all of the proper gauge, can both sides handle a 30Amp load?

 

[llburg]

Y-Style. Assuming the cable is properly constructed and terminated, is there any risk of overloading the neutral? What about maximum current draw? Assuming the wires are all of the proper gauge, can both sides handle a 30Amp load?

According to my limited understanding of electrical theory, if the load on each phase is perfectly balanced, then there will be no current on the neutral. However, if the loads are severely unbalanced, it can overload the neutral.

 

[RonHebbard]

Y-Style. Assuming the cable is properly constructed and terminated, is there any risk of overloading the neutral? What about maximum current draw? Assuming the wires are all of the proper gauge, can both sides handle a 30Amp load?

Hello Mr. Tuba;

Look at it this way:

Whether your source is single phase, 120 - 0 - 120 Volts measuring 240 Volts between the two hot legs and 120 Volts between either hot leg and neutral
OR
three phase, 120 / 208 Volts measuring 208 Volts between any two hot legs and 120 Volts between either hot leg and neutral, your worst case neutral current should occur when only one side of your 'two-fer' is loaded in which case your neutral's current should equal the current in your loaded hot leg.
Single phase or three phase, as you load the second side of your adapter you're providing an alternative path for the currents on your hot legs. In a perfect situation, if both hot legs were loaded equally, your neutral would see zero current.

O.K.; the above is a very 'bare bones' oversimplification and I'm sure many will be along shortly to pick away at what I've written.

Let's dream up something really ugly.
If both of your hot legs were sourced from the same side of a single phase source, or two circuits from a common phase, THEN your neutral current would add to the total of your two loads and, potentially, overload your neutral conductor; potentially depending upon your total current draw.

Hopefully this'll sort your thinking and I'm sure many others will pile on shortly.
I suppose you could also think about how the wiring works for typical electric stoves and driers.

EDIT: Mr. llburg and I were typing at the same time.
I'll expand on Mr. llburg's posting.
Your worst imbalance should occur with one side of your 'two-fer' loaded and the other side unplugged.
In this case, assuming zero faults, your neutral current should equal the current in your loaded hot leg.

Toodleoo!
Ron Hebbard

 

[epimetheus]

Nobody has mentioned triplen harmonics yet. If both L5-30 legs are feeding switch-mode power supplies or the like, you can have triplen harmonics on the neutral that can sum to cause the neutral current to be larger than the phase current. I think this would not be a very likely scenario to find yourself in, but something to be aware of none-the-less.

 

[JD]

Hard to see triplen becoming a problem on two legs. With a worst case crest of 40% (or 140% of capacity) with three legs in play, you now remove one and take out 33% of the source current. Given constant current ratings, the best I could fathom would be a 7% crest (or 107% depending on how you look at it.) Technically, your triplen in this case is 120 Hz, but patterned at the 180 Hz frequency, with one hump missing....
So, the only time you would exceed 100% is if you were running the circuit at it's full 30 amp capacity on both legs, and ran your dimmers at liner 50% so you did not have a full cancel. You could at that time develop 32.1 amps on the neutral if both legs each had 3600 watt/hs on them. Switch mode supplies would have about the same overlap as they would be conducting during a 120 degree phase angle on the opposing leg. In this case, crest would be 133%, less the missing third leg, or about 100% rating, so no problem. Of course all of this would be nullified if run off a standard branch circuit which gets de-rated by 20%. In that case, neither scenario would crest the neutral above 100%