Can You Tap 120V Off a 208V Circuit?

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ASG

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I have a 3-phase circuit feeding a load (let's say an AC unit). If I send it with a neutral, can I tap one phase of that circuit, add a 1P-20A enclosed circuit breaker and use that to feed my condensate pump and leak detector?
 
ASG said:
I have a 3-phase circuit feeding a load (let's say an AC unit). If I send it with a neutral, can I tap one phase of that circuit, add a 1P-20A enclosed circuit breaker and use that to feed my condensate pump and leak detector?
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IMO, as long as you abide by all of the rules, no problem. However, if you really need 20A to feed the condensate pump it might well be hard to abide by all of the rules.
 
petersonra said:
IMO, as long as you abide by all of the rules, no problem. However, if you really need 20A to feed the condensate pump it might well be hard to abide by all of the rules.
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I agree.

A quick dis-qualifier is whether OP'er is talking line-side or load-side of the branch-circuit OCPD. Tapping load-side is very, very limited; definitely does not permit tapping A/C circuits for the equipment stated.

Though I wonder, if the tap occurs after the A/C equipment supply terminals, does it fall under the purview of the NEC??? You'd not be tapping premises wiring.
 
petersonra said:
IMO, as long as you abide by all of the rules, no problem. However, if you really need 20A to feed the condensate pump it might well be hard to abide by all of the rules.
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Can you explain further on this?

As a side note, the CP/leak detector are normally fed via a 20A CB but they are very small.
 
ASG said:
Can you explain further on this?

As a side note, the CP/leak detector are normally fed via a 20A CB but they are very small.
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You started by asking what seemed to be a hypothetical question... :huh:

For the rules, a good place to start is 240.4(E)...
 
Smart $ said:
Though I wonder, if the tap occurs after the A/C equipment supply terminals, does it fall under the purview of the NEC??? You'd not be tapping premises wiring.
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I am all for your plan as soon as I see something from the manufacturer that blesses that modification and provides new MCA / MOCP numbers for the label. :)

(By the way, some of the wall mount split systems have an optional condensate pump that is powered from the unit.)
 
iwire said:
I am all for your plan as soon as I see something from the manufacturer that blesses that modification and provides new MCA / MOCP numbers for the label. :)

(By the way, some of the wall mount split systems have an optional condensate pump that is powered from the unit.)
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;):D
 
iwire said:
I am all for your plan as soon as I see something from the manufacturer that blesses that modification and provides new MCA / MOCP numbers for the label. :)

(By the way, some of the wall mount split systems have an optional condensate pump that is powered from the unit.)
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In our office we typically size the wire and breaker to the MOCP. Most condensate pumps are a couple of hundred watts. So as long as the load of the pump isn't so large that it would increase the size of load so much that it would trip the breaker, I don't see why the manufacturer would have to be involved.
 
ASG said:
In our office we typically size the wire and breaker to the MOCP. Most condensate pumps are a couple of hundred watts. So as long as the load of the pump isn't so large that it would increase the size of load so much that it would trip the breaker, I don't see why the manufacturer would have to be involved.
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I was responding to Smarts suggestion of tying it into the factory wiring of the unit. If you did that the inspector could without a doubt ask for the manufacturer to approve it.
 
ASG said:
I have a 3-phase circuit feeding a load (let's say an AC unit). If I send it with a neutral, can I tap one phase of that circuit, add a 1P-20A enclosed circuit breaker and use that to feed my condensate pump and leak detector?
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Are you trying to tap the AC unit's branch circuit or feeder circuit conductors?
 
Well everyone knows I love to cut and paste so here are the article 100 definitions..........:)



Branch Circuit. The circuit conductors between the final
overcurrent device protecting the circuit and the outlet(s).
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Feeder. All circuit conductors between the service equipment,
the source of a separately derived system, or other
power supply source and the final branch-circuit overcurrent
device.
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If I recall it has been hotly debated if using a fused disconnect at the unit change the circuit from the panel from a branch circuit to a feeder.
 
iwire said:
Well everyone knows I love to cut and paste so here are the article 100 definitions..........:)
...

If I recall it has been hotly debated if using a fused disconnect at the unit change the circuit from the panel from a branch circuit to a feeder.
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That would bring into question whether the fused disconnect is supplementary protection or not. What qualifies as supplementary protection is not clearly defined, but we still have a provision for it...

240.10 Supplementary Overcurrent Protection. Where
supplementary overcurrent protection is used for luminaires,
appliances, and other equipment or for internal circuits
and components of equipment, it shall not be used as
a substitute for required branch-circuit overcurrent devices or
in place of the required branch-circuit protection. Supplementary
overcurrent devices shall not be required to be readily
accessible.
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Smart $ said:
That would bring into question whether the fused disconnect is supplementary protection or not. What qualifies as supplementary protection is not clearly defined, but we still have a provision for it...
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If we install said fused disconnect to comply with the units labeling which is the 'branch circuit selection current' (440.2) it must not be supplementary protection but branch circuit protection .... right? :huh:


I think we think to much. :p
 
iwire said:
If we install said fused disconnect to comply with the units labeling which is the 'branch circuit selection current' (440.2) it must not be supplementary protection but branch circuit protection .... right? :huh:
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Well that's certainly one train of thought... and I would go with it. However, the inspector's train of thought may differ. :happyyes:

I think we think to much. :p
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In cases where we have to account for what others may think, I believe we have to. Thinking too much is when it carries over into matters that don't concern what others think... :D
 
iwire said:
If we install said fused disconnect to comply with the units labeling which is the 'branch circuit selection current' (440.2) it must not be supplementary protection but branch circuit protection .... right?
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You would install a fused disconnect to comply with the branch circuit selection current or the rated load current, whichever is greater.

I don't think I've ever seen a unit with a labeled "branch circuit selection current" though.
 
david luchini said:
You would install a fused disconnect to comply with the branch circuit selection current or the rated load current, whichever is greater.

I don't think I've ever seen a unit with a labeled "branch circuit selection current" though.
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I often wondered whether "branch circuit selection current" is a Code equivalent to nameplate minimum circuit ampacity (MCA). Certainly wouldn't be the first time Code and listing standards have had a terminology disparity.
 
Smart $ said:
I often wondered whether "branch circuit selection current" is a Code equivalent to nameplate minimum circuit ampacity (MCA). Certainly wouldn't be the first time Code and listing standards have had a terminology disparity.
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It is not. Minimum circuit ampacity are branch circuit selection current are separate items.

Take a look at 440.32, for instance. MCA is determined by 125% of the RLA or 125% of the BCSC, whichever is greater.
 
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