5 ms·

> Even though the 14-50R outlet is technically a 50A outlet, when used as a kitchen range plug, they are often wired on a 40A circuit. This is permitted by the

> Even though the 14-50R outlet is technically a 50A outlet, when used as a kitchen range plug, they are often wired on a 40A circuit. This is permitted by the Canadian Electrical Code rule 26-744 5). I wonder if the US National Electric Code allows this.

egberts1 2y ago
The “50” in 14-50R refers to the maximum "rated" amperage allowed through the receptacle. Load-wise, to avoid melted connector, you don't plug something with load capacity of more than 37-ish ampere thru this 14-50R receptacle. The OP is confusing load rating vs. capacity rating. However, computed loads are always adequately under the breaker size, and beneath wire capacity, and below the receptacle rating, all three and each components of a circuit. Many urban building codes often demand the 14-50R receptacle to match the 6/3 COPPER (not Romex) wire and 50A breaker size, often as a response to mass introduction of EV. NEC 2018/2022 is unchanged about the permissible used of 50A-rated receptacle with smaller 40A breaker but NEC code firmly states that a breaker cannot exceed 8/3 AWG wire rated capacity and many types of 8/3 sheathing barely supports 50A; that's because NEC is all about load-rating, well beneath its rated capacity. Naturally, in light of those NEC "restrictions", if an EV charger calls for a 50A RATED circuit (because charger performs at nominal load operation at 37A-ish, you'll want all three components of the circuit to each carry 50A. This is the part where the former electric stove/range 8/3 wire failed to meet the new EV charger's demand. If the EV charger is rated for 60A but operates nominally at 46A, DO NOT go the 50A installaion route. Go with 60A. Operating your load capacity near its rated capacity is potential meltdown situation, especially if weather turns hot, Hot, HOT! Also for 50A rated EV charger in the high-temperature area (garage), 8 AWG copper wire and 6 AWG aluminum wire are not NEC-code recommended despite having the 50 AMP to 60 AMP ampacity rating (NEC code); go with 6/3 copper. For most residential garage having 50A-rated EV charger, that means 6/3 (non-Romex) copper AWG, 50A breaker, and 14-50R receptacle. Open-air carport and year-round cooler weather region can NEC-wise get away with (but local/urban electrical code may prevent) the use of 8/3 AWG copper (but no aluminum) wires.
- Kirby64 2y ago
  What's your math on this? I don't understand how you're getting to 37A. A 50 amp rated outlet (backed by a 50 amp rated breaker, and wire capable of handling 50 amps) is fully NEC compliant if you run it for 40 amps continuously (80% derating) or 50 amps temporarily (which NEC defines as a load expected to continue for 3 hours or more). EV chargers fall under the 80% derating. I'm not aware of any EV charger that uses 37A. They either support 40A (80% of 50A), 32A (80% of 40A), or 48A (80% of 60A).
  - egberts1 2y ago
    I did take liberty here in saying 37A-ish (40A is code) because that's what some national fire marshalls are reporting about hot garage and reuse of range-type wiring for new purpose of EV charging. It's the wire material and size issue in hot area.
    - Kirby64 2y ago
      But, if it supports 40A charging it'll charge at 40 amps unless you back off the charging rate (which nobody does, typically). You'd always assume 40 amps for circuit purposes.
      - egberts1 2y ago
        See @quickthrowman's comment for detailed breakdown on high-temperature and copper wire.
  - quickthrowman 2y ago
    > What's your math on this? I don't understand how you're getting to 37A You have to derate conductors installed in ambient temperatures greater than 86F. I would definitely use NM-B 6/2G (or 6/2G MC cable) for a NEMA 14-50R in a garage, just to account for derating since you get to start at 75A for #6 rated for 90C. The first derating factor is .94 for ambient temps between 87-95F, .94 times 40A is 37.6A if you use the 75C column. I think NM cable is rated for 90C, so if you derate #8 from 55A at .67 to account for a much higher temp of 120-130F, you get 36.85A. 310.15 (B)(1) Ambient Temperature Correction Factors Based on 30°C (86°F) For ambient temperatures other than 30°C (86°F), multiply the allowable ampacities specified in the ampacity tables by the appropriate correction factor shown below. https://conduit.site/tables/table-310.15-b-1.php https://conduit.site/tables/table-310.15-b-1.php
quickthrowman 2y ago
Yes, but only for circuits with multiple outlets, an individual branch circuit must use a wiring device not less than the ampacity of the branch circuit. You are allowed to use 40A and 50A receptacles on a multi-outlet 40A circuit. You’re also allowed to use 15A and 20A receptacles on a multi-outlet 20A circuit. Table 210.21(B)(3) of the NEC https://up.codes/s/outlet-devices https://up.codes/s/outlet-devices
- Kirby64 2y ago
  You have it backwards. If you have a single receptacle on a branch circuit then the OCPD (breaker) must be sized at or under the receptacle. I.e., a 50 amp outlet can be backed with a 50 amp breaker or anything smaller. You could even have a 20 amp breaker (and 12 gauge wire) backing a 50 amp outlet, which is common for welding applications where peak currents are extremely high on arc start but continously are much lower. There's a specific carve out for welders as well, but it applies to any outlet.

egberts1 2y ago

The “50” in 14-50R refers to the maximum "rated" amperage allowed through the receptacle. Load-wise, to avoid melted connector, you don't plug something with load capacity of more than 37-ish ampere thru this 14-50R receptacle. The OP is confusing load rating vs. capacity rating. However, computed loads are always adequately under the breaker size, and beneath wire capacity, and below the receptacle rating, all three and each components of a circuit. Many urban building codes often demand the 14-50R receptacle to match the 6/3 COPPER (not Romex) wire and 50A breaker size, often as a response to mass introduction of EV. NEC 2018/2022 is unchanged about the permissible used of 50A-rated receptacle with smaller 40A breaker but NEC code firmly states that a breaker cannot exceed 8/3 AWG wire rated capacity and many types of 8/3 sheathing barely supports 50A; that's because NEC is all about load-rating, well beneath its rated capacity. Naturally, in light of those NEC "restrictions", if an EV charger calls for a 50A RATED circuit (because charger performs at nominal load operation at 37A-ish, you'll want all three components of the circuit to each carry 50A. This is the part where the former electric stove/range 8/3 wire failed to meet the new EV charger's demand. If the EV charger is rated for 60A but operates nominally at 46A, DO NOT go the 50A installaion route. Go with 60A. Operating your load capacity near its rated capacity is potential meltdown situation, especially if weather turns hot, Hot, HOT! Also for 50A rated EV charger in the high-temperature area (garage), 8 AWG copper wire and 6 AWG aluminum wire are not NEC-code recommended despite having the 50 AMP to 60 AMP ampacity rating (NEC code); go with 6/3 copper. For most residential garage having 50A-rated EV charger, that means 6/3 (non-Romex) copper AWG, 50A breaker, and 14-50R receptacle. Open-air carport and year-round cooler weather region can NEC-wise get away with (but local/urban electrical code may prevent) the use of 8/3 AWG copper (but no aluminum) wires.

Kirby64 2y ago
What's your math on this? I don't understand how you're getting to 37A. A 50 amp rated outlet (backed by a 50 amp rated breaker, and wire capable of handling 50 amps) is fully NEC compliant if you run it for 40 amps continuously (80% derating) or 50 amps temporarily (which NEC defines as a load expected to continue for 3 hours or more). EV chargers fall under the 80% derating. I'm not aware of any EV charger that uses 37A. They either support 40A (80% of 50A), 32A (80% of 40A), or 48A (80% of 60A).
- egberts1 2y ago
  I did take liberty here in saying 37A-ish (40A is code) because that's what some national fire marshalls are reporting about hot garage and reuse of range-type wiring for new purpose of EV charging. It's the wire material and size issue in hot area.
  - Kirby64 2y ago
    But, if it supports 40A charging it'll charge at 40 amps unless you back off the charging rate (which nobody does, typically). You'd always assume 40 amps for circuit purposes.
    - egberts1 2y ago
      See @quickthrowman's comment for detailed breakdown on high-temperature and copper wire.
- quickthrowman 2y ago
  > What's your math on this? I don't understand how you're getting to 37A You have to derate conductors installed in ambient temperatures greater than 86F. I would definitely use NM-B 6/2G (or 6/2G MC cable) for a NEMA 14-50R in a garage, just to account for derating since you get to start at 75A for #6 rated for 90C. The first derating factor is .94 for ambient temps between 87-95F, .94 times 40A is 37.6A if you use the 75C column. I think NM cable is rated for 90C, so if you derate #8 from 55A at .67 to account for a much higher temp of 120-130F, you get 36.85A. 310.15 (B)(1) Ambient Temperature Correction Factors Based on 30°C (86°F) For ambient temperatures other than 30°C (86°F), multiply the allowable ampacities specified in the ampacity tables by the appropriate correction factor shown below. https://conduit.site/tables/table-310.15-b-1.php https://conduit.site/tables/table-310.15-b-1.php

quickthrowman 2y ago

Yes, but only for circuits with multiple outlets, an individual branch circuit must use a wiring device not less than the ampacity of the branch circuit. You are allowed to use 40A and 50A receptacles on a multi-outlet 40A circuit. You’re also allowed to use 15A and 20A receptacles on a multi-outlet 20A circuit. Table 210.21(B)(3) of the NEC https://up.codes/s/outlet-devices https://up.codes/s/outlet-devices

Kirby64 2y ago
You have it backwards. If you have a single receptacle on a branch circuit then the OCPD (breaker) must be sized at or under the receptacle. I.e., a 50 amp outlet can be backed with a 50 amp breaker or anything smaller. You could even have a 20 amp breaker (and 12 gauge wire) backing a 50 amp outlet, which is common for welding applications where peak currents are extremely high on arc start but continously are much lower. There's a specific carve out for welders as well, but it applies to any outlet.