The existing building had 120/240V 1ph service and now is being upgraded to 120/208V 3ph service...Electrician is suggesting reusing all existing 120/240V 1ph rated panels by backfeeding from 120/208V. Is this not a code violation? All labels on panels are 120/240 but the actual power supply will be 120/208V. I couldn't find the right code section for this. Thanks.
Code Violation?
- Thread starter elec_eng
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renosteinke
Senior Member
- Location
- NE Arkansas
Breaker and panel ratings will allow for the (former) 240 circuits to be fed by 208.
The only real listing issue would arise were this a 240/120 3 phade delta ... but that's not the case here, so there's no sense muddying the waters. In any event, feeding 1-phase panels from the new 3-phase service is not an issue.
Where there MIGHT be an issue is with certain appliances. For example, any sort of heating element will really suffer from the lower voltage, and the customer might have to replace them. For example, the 'booster' heater in a restaurant dishwasher will no longer make the water hot enough.
Another thing that may suffer is the air conditioning; many of those are actually rated at 240v - for which 208 isn't enough. Remember that motors are designed to operate within 10% of their nameplate voltage (actual delivered volts needs to be within 10% of the nameplate).
The only real listing issue would arise were this a 240/120 3 phade delta ... but that's not the case here, so there's no sense muddying the waters. In any event, feeding 1-phase panels from the new 3-phase service is not an issue.
Where there MIGHT be an issue is with certain appliances. For example, any sort of heating element will really suffer from the lower voltage, and the customer might have to replace them. For example, the 'booster' heater in a restaurant dishwasher will no longer make the water hot enough.
Another thing that may suffer is the air conditioning; many of those are actually rated at 240v - for which 208 isn't enough. Remember that motors are designed to operate within 10% of their nameplate voltage (actual delivered volts needs to be within 10% of the nameplate).
I agree with you in the engineering stand point of view..but how about the label on the panels? It will still have 120/240V label but supplied by 120/208V system..Will it not cause a safety issue later on?
- Location
- Illinois
- Occupation
- retired electrician
The use of single phase panels with two ungrounded conductors and the grounded conductor from a 208/120Y system is common. I have never seen a single phase panel with a 208/120 label. Do they exist?
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
I was going to say, most every panel label I have seen says Maximum voltage.
However the Siemens panel, next to my desk, says 120/240 1PH 3W, 120/208 1PH 3W.
The Cutler Hammer, one in the shop, says For Single Phase 120/240 1PH 3W, 208Y/120 3W.
From the UL White Book:
"Two-pole independent-trip breakers and single-pole breakers with handle ties that are rated 120/240 V ac have been investigated for use in line-to-line single-phase circuits or line-to-line lighting and appliance branch circuits connected to 3-phase, 4-wire systems, provided the systems have a grounded neutral and the voltage to ground does not exceed 120 V."
"Two-pole independent-trip breakers and single-pole breakers with handle ties that are rated 120/240 V ac have been investigated for use in line-to-line single-phase circuits or line-to-line lighting and appliance branch circuits connected to 3-phase, 4-wire systems, provided the systems have a grounded neutral and the voltage to ground does not exceed 120 V."
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
I wouldn't put that saying to an air compressor unless to motor is design to run on 208, seen to many burn up the motor.
Many motors with high toque requirements will require the correct voltage, such as a 200 volt motor for a 208 installation
Ingersol-Rand supplies 200V single voltage motors for compressors intended for 208V operation, they do not supply "tri-volt" (200-230/460V) motors.
- Location
- Bremerton, Washington
But its a violation of 110.3(B), Mike Holt has a graphic on this, and 240 V motors are not happy on 208
Most motors I have seen were rated 208/240. With respective FLA.
Motors will put out the power needed, if the pump requires 5HP the motor will put out that 5 HP wether it's a 3HP motor (it'll burn) or 10HP (will run somewhat higher than 1/2 FLA). At the same time the ampacity on an inductive load will be inverse proportional to the voltage (unlike resistive loads where the ampacity is direct proportional to voltage). So running a motor on a higher voltage will cause the ampacity to drop, how much higher voltage you can run it on depends on the insulation VS the voltage. Obviously we all know that 5KV requires much thicker insulation not because the ampacity but because the electrons on 5KV will jump through the insulation 600V don't.
So if a motor is rated strictly 240 and will be run on 208 it'll overheat IF run at max horsepower (keep in mind most times engineers oversize motors to be safe). On the other hand if it's rated strictly 208 and will be run on 240 the insulation will get compromised eventually with time.
Last, let's not forget motor designers will take in considerations voltage drops, overvoltage and overload, so technically there's a little wiggle room even if a motor is rated strictly a certain voltage.
But again, I don't think I have seen a motor rated strictly for 240 or 208.
Motors will put out the power needed, if the pump requires 5HP the motor will put out that 5 HP wether it's a 3HP motor (it'll burn) or 10HP (will run somewhat higher than 1/2 FLA). At the same time the ampacity on an inductive load will be inverse proportional to the voltage (unlike resistive loads where the ampacity is direct proportional to voltage). So running a motor on a higher voltage will cause the ampacity to drop, how much higher voltage you can run it on depends on the insulation VS the voltage. Obviously we all know that 5KV requires much thicker insulation not because the ampacity but because the electrons on 5KV will jump through the insulation 600V don't.
So if a motor is rated strictly 240 and will be run on 208 it'll overheat IF run at max horsepower (keep in mind most times engineers oversize motors to be safe). On the other hand if it's rated strictly 208 and will be run on 240 the insulation will get compromised eventually with time.
Last, let's not forget motor designers will take in considerations voltage drops, overvoltage and overload, so technically there's a little wiggle room even if a motor is rated strictly a certain voltage.
But again, I don't think I have seen a motor rated strictly for 240 or 208.
- Location
- Massachusetts
Again, as per the original post, changing the panels to 120/208 wouldn't do anything to help this hypothetical situation.
a) Original system is 120/240.
b) New system will be 120/208
c) Electrician suggested using original panels.
Now, depending on how many panels there are existing along with what loads may be added, the balancing of the loads/phases may come into play and would require consideration.
I'm confused. Why would you have to backfeed the panels to reuse them?
I assume there would be a main 3 phase panel, and that panel would feed all the reused panels as subpanels. Is that right?
Doesn't a panel have to be listed for backfeeding, or isn't there a kit to install on a backfed breaker? Something to keep it from pulling away from the bus during a short circuit?
I assume there would be a main 3 phase panel, and that panel would feed all the reused panels as subpanels. Is that right?
Doesn't a panel have to be listed for backfeeding, or isn't there a kit to install on a backfed breaker? Something to keep it from pulling away from the bus during a short circuit?
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