NEMA 14-50P PLUG
- Thread starter fifty60
- Start date
- Status
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Can you use a disconnect and direct wire the unit?
- Location
- Massachusetts
You may have to go with something other than the L14
I like these products. http://www.meltric.com/
They are well constructed and durable.
Keep in mind a male and female set may be about $300.00
I like these products. http://www.meltric.com/
They are well constructed and durable.
Keep in mind a male and female set may be about $300.00
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
The 3HP limit is part of the design spec. HP ratings of plugs and receptacles are based on Locked Rotor Amps, not running amps, hence the much smaller rating than the amp rating would suggest.
Are you trying to use this for 3 phase though? It is NOT a 3 phase plug! For 3 phase you need a 15-50, which is rated for 7.5HP
Are you trying to use this for 3 phase though? It is NOT a 3 phase plug! For 3 phase you need a 15-50, which is rated for 7.5HP
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Since the 14-50 specification requires the ability for the connector to interrupt its full rated load, the combination of motor inrush and inductive kick on disconnect probably force all of the manufacturers to limit the motor service HP to a lower value than the resistive current capability would otherwise convert to in HP.
What is the nema 14-50 then? It has 3 conductors and a ground?
Everything in my machine is single phase, but the incoming supply is 3 phase. The machine's plug will mate with a 208V/3PH/60Hz receptacle. The machine is wired so that I have phase to phase for 208V single phase loads. There are no 3 Phase loads in the machine.
How would I analyze the HP requirement then? Which plug configuration would I use? I am a little confused on this one...
Everything in my machine is single phase, but the incoming supply is 3 phase. The machine's plug will mate with a 208V/3PH/60Hz receptacle. The machine is wired so that I have phase to phase for 208V single phase loads. There are no 3 Phase loads in the machine.
How would I analyze the HP requirement then? Which plug configuration would I use? I am a little confused on this one...
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Does the machine come with a NEMA 14-50P attached to it already? If so there is no other socket specification that it will mate with.
Does the machine have a single motor larger than 3HP or are there multiple motors and resistive loads in some combination?
Is there a VFD-like motor controller built in, or will you just be starting the motor across the line?
All of this will affect whether you can use the NEMA 14-50 and still comply with the usage limits marked on the plug and receptacle.
Is it correct that the machine will not be drawing more than 50A from any phase conductor during normal (non-starting) operation?
- Location
- Massachusetts
Two hots a neutral and a ground.
It should not be used for three hots and a ground
You would want a 15-50
zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
It has one EGC, one grounded conductor, and two 'hot' conductors ("125/250v"). It should not have three 'hot' conductors.
If the machine has a 14-50p, then it can't mate with a proper 208V/3PH receptacle since that would not be a 14-50, more likely a 15-50, but that doesn't have a neutral/grounded conductor (so you can't get 120v from it). OTOH, if the machine doesn't actually need real 3-phase, then it doesn't matter whether the supply is two legs of a 3-phase system or two legs of a 120/240v single phase system. Both of them can be applied to a 14-50.
Customer is specifying the plug and receptacle. They say they have 208V 3Ph 60Hz supply but want to use the 14-50 R&P. So, they cannot actually have the 208V 3PH 60Hz and provide a 14-50R?
The machine does not have any 3PH loads, nor does it have any 120V loads (other than the control circuit derived from a control transformer). I am not using any neutrals. 208V phase to phase is how the machine is designed, all single phase from a 3PH supply.
If the customer has 208V 3PH 60Hz then they can't have a 14-50R? The machine could operate from a 14-50R just fine, as long as the loads are seeing 208V single phase everything will be fine.
I have two separate 2HP motors for a total combined 4HP. There are also resistive loads and a 1KVA general purpose transformer. No VFD's. The machine will need to have a 45A main Circuit Breaker.
The machine does not have any 3PH loads, nor does it have any 120V loads (other than the control circuit derived from a control transformer). I am not using any neutrals. 208V phase to phase is how the machine is designed, all single phase from a 3PH supply.
If the customer has 208V 3PH 60Hz then they can't have a 14-50R? The machine could operate from a 14-50R just fine, as long as the loads are seeing 208V single phase everything will be fine.
I have two separate 2HP motors for a total combined 4HP. There are also resistive loads and a 1KVA general purpose transformer. No VFD's. The machine will need to have a 45A main Circuit Breaker.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
OK then, if you are NOT connecting any 3 phase loads, the 14-50 could technically be OK from the voltage / phase standpoint, you would not however run all 3 phases to the receptacle, you wouldl only run 2 of the 3 phases, plus neutral (and ground), even if the machine is not using the neutral. You have to be careful when running receptacles, because once it is installed, someone LATER could ASSume that because it is a NEMA L14-50, it will have 2 hots and a neutral.
But it will still not be rated for more than 3HP, because that would be 3HP at 208V single phase, not 3HP at 208V 3 phase, and you have 4HP at 208V single phase. You are exceeding the listed rating of the device, end of story. It will have to be hard wired, or use a pin and sleeve connecter as previously suggested.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
They can use a 3-phase 208Y/120 service and you would only wire two of the three phase wires to the 14-50R receptacle.
If they wanted you to wire all three phases and leave out the neutral (grounded conductor) that would be a violation of the listing of the receptacle.
I would not stick my neck out with respect to an AHJ approving it, but IMHO your two 2HP motors will not cause use of the 14-50 to be particularly hazardous. It might be a problem with the UL-listed usage of the receptacle as marked by the manufacturer.
And if both motors will start at the same time, the heating of the terminals in the connectors may require you to use higher temp wire and/or larger wire size (within the limits that the terminals will accept.)
- Location
- Massachusetts
If I was the one asked to do this I would be asking for a spec sheet or the model and manufacturer of the equipment before I assumed anything.
Could I use a 15-50P/R since the machine is designed to work from a 3 phase supply? The loads are single phase and each branch is wired hot to hot as described before. The machine is designed for the single pahse loads to use 3 phase coming in to a distribution block
The 15-50P/R are rated for 7.5HP? I cannot find any charts online that have the NEMA and HP ratings. Does the fact that all of the loads are single phase affect the 7.5HP rating of the plug/receptacle? Can I use the 15-50P/R for 4HP worth of single phase loads?
The 15-50P/R are rated for 7.5HP? I cannot find any charts online that have the NEMA and HP ratings. Does the fact that all of the loads are single phase affect the 7.5HP rating of the plug/receptacle? Can I use the 15-50P/R for 4HP worth of single phase loads?
found a good chart that has the HP ratings...http://www.cooperindustries.com/content/dam/public/wiringdevices/BuyersGuides/AHBG/R/AHBG-R-Sec.pdf
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
AHA! Now we find out the whole story. The machine has multiple single phase loads which are designed to be spread out over all three phases based on internal wiring from the three-phase terminal strip. That would have been nice to be clear on at the start.
Yes, the 15-50 will be exactly what you need. Although if somebody unplugging the cord accidentally could have bad effects, you may want to use the twist lock version instead.
The popularity of the 14-50 for dryers and RVs makes it visible to the customer, but it is definitely not the right connector for the job.
Oh, and a single three-phase motor of 7.5 HP will result in roughly the same loading per phase wire as three 2.5 HP motors each on a single phase, so you should be OK with two 2 HP motors on separate phases instead.
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