Common Trips and Handle ties

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brother

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I have seen this happen again where 1 leg of the 240v single phase circuit was tripped and the other was not in this house. They did have a 'listed' handle tie. I know NEC 240.15(B)(2) allows one to use the handle ties and not a require a common trip breaker for this scenario but it seems to create more of a hazard is what I have seen lately.

Was there a reason why the NEC allowed handle ties for this? just curious about the history.
 
When the Code is discussing the use of the breaker as a manual disconnect (e.g. for MWBC) the handle tie and the common trip serve exactly the same purpose.
Where the code wants simultaneous disconnect of all ungrounded conductors in the event of a fault (line to line load), only common trip will do the job.
Different Code sections different requirements.
Simple as that IMHO.

And handle ties need to be accepted or recognized, not necessarily listed.
 
infinity said:
Couldn't you use a handle tie for a line to line load?
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You can use a handle tie unless the code (or the job specs or manufacturer's instructions for the load) requires a simultaneous break of all ungrounded conductors in the event of a fault.
Clearly simple fuses cannot do that, but breakers can.
 
infinity said:
Couldn't you use a handle tie for a line to line load?
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Hmm, your question made me look it up. 240.15(B) (2011) generally requires a circuit breaker to automatically open all ungrounded circuit conductors with some exceptions. The exceptions seem to cover all cases where the ungrounded conductors are 120V to ground to less. So for a 240V circuit from single phase 120/240, two single pole breakers with a handle tie are allowed.

Cheers, Wayne
 
brother said:
Can anyone name a situation in the code where a common trip, (not handle tie) would be required for a single phase 120/240 load? I used to think that 240v water heaters needed a common trip, but apparently not.
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For a straight 240 volt load (water heater) or a MWBC serving line to neutral loads (two 120 volt circuits) a common trip or a two single pole CB's with a handle tie are acceptable. If the load is 120/240 (like a clothes dryer) then a common trip is required. {240.15(B)(1)&(2)}
 
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infinity said:
For a straight 240 volt load (water heater) or a MWBC serving line to neutral loads (two 120 volt circuits) a common trip or a two single pole CB's with a handle tie are acceptable. If the load is 120/240 (like a clothes dryer) then a common trip is required. {240.12(B)(1)&(2)}
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I am looking in the 2014 NEC 240.12 and I do not see what you are referring to. What code year are you using??
 
brother said:
Ok, Im looking at that one too. I am still not seeing where a dryer would be required to have a common trip, and not be allowed to use a handle tie. Unless I am reading this wrong? it says Line to Line connected loads.
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It says only L to L loads, a typical dryer has both L to L and L to. N loads.

(BTW- I also had to read it a few times to see what Rob had seen, it's why I was pretty sure it was .15).
 
Let's separate the terms handle ties and common trip. If you take two or three 1p breakers and install them side by side and you want to make it so you have no choice but to turn all breakers on and off as a set you would install a suitable handle tiie. But will the handle tie not do is to open the both or all breakers ties together with the handle tie should one of the 1p breakers trip.
With multiple breakers that look like they are tied together with a handle tie and marked/labeled as common trip that is an indication that the trip mechanisms are tir together internally such that should one pole trip that pole also trips the other pole(s) at the same time.
If it is required to open all poles automatically then you have no other option than to use a multiple breaker with a common trip.
What comes to mind is a home run circuit where if you would like to work on one circuit you need to turn off both circuits to prevent a shock hazard. The circuits being feed by two 1p breakers with a handle tie. Shoul 1 ckt call for a trip that circuit will not open the other circuit needlessly.
Yes, could could use a 2p common trip breaker but should one ckt call for a trip it woulkd needlessly trip the other circuit.
 
templdl said:
Let's separate the terms handle ties and common trip. If you take two or three 1p breakers and install them side by side and you want to make it so you have no choice but to turn all breakers on and off as a set you would install a suitable handle tiie. But will the handle tie not do is to open the both or all breakers ties together with the handle tie should one of the 1p breakers trip.
With multiple breakers that look like they are tied together with a handle tie and marked/labeled as common trip that is an indication that the trip mechanisms are tir together internally such that should one pole trip that pole also trips the other pole(s) at the same time.
If it is required to open all poles automatically then you have no other option than to use a multiple breaker with a common trip.
What comes to mind is a home run circuit where if you would like to work on one circuit you need to turn off both circuits to prevent a shock hazard. The circuits being feed by two 1p breakers with a handle tie. Shoul 1 ckt call for a trip that circuit will not open the other circuit needlessly.
Yes, could could use a 2p common trip breaker but should one ckt call for a trip it woulkd needlessly trip the other circuit.
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I understand how the common trip works. Just trying to clarify what the NEC actually says about it. As in IWIREs example i have seen many new jobs in residential where they used a handle tie. For 30amp dryer circuits instead of a common trip. So technically it appears the handle tie would be violation.
But one would ask why is it ok for mwbc can have a handle tie but the dryer circuits could not when in thoery they r the sane.
 
brother said:
But one would ask why is it ok for mwbc can have a handle tie but the dryer circuits could not when in thoery they r the sane.
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I was wondering the same thing.

The way the rules work out for 120/240 single phase is that handle ties are sufficient if the circuit has either only L-L loads or only L-N loads. If the circuit has both L-L loads and L-N loads, then a common trip breaker is required. So what is the hazard of only one pole tripping on a circuit with both L-L and L-N loads, that does not also exist in one of the other two cases?

Cheers, Wayne
 
brother said:
I am looking in the 2014 NEC 240.12 and I do not see what you are referring to. What code year are you using??
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Yes it should have said 240.15 not 240.12. I fixed it, thanks for pointing out the error.

brother said:
I understand how the common trip works. Just trying to clarify what the NEC actually says about it. As in IWIREs example i have seen many new jobs in residential where they used a handle tie. For 30amp dryer circuits instead of a common trip. So technically it appears the handle tie would be violation.
But one would ask why is it ok for mwbc can have a handle tie but the dryer circuits could not when in thoery they r the sane.
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A MWBC is really just two 120 volts circuits sharing a neutral. Until a few code cycles ago a handle tie was not even required for a MWBC.
 
infinity said:
Yes it should have said 240.15 not 240.12. I fixed it, thanks for pointing out the error.



A MWBC is really just two 120 volts circuits sharing a neutral. Until a few code cycles ago a handle tie was not even required for a MWBC.
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That is true, and yet it still doesn't explain the NEC's reasoning ;-) . I found an interesting article dated a few years back (2003) about common trip and handle ties. Apparently at one point they were considering requiring common trip for all line to line loads.

http://ecmweb.com/content/common-misunderstandings-overcurrent-protection

The fundamental requirement of 240.20(B) is that the circuit breaker shall open all ungrounded conductors of the circuit. In other words, it calls for common trip. The section provides the following exceptions to allow the use of single-pole circuit breakers with handle ties:

•In multiwire branch circuits


•On circuits with line-to-line connected loads of grounded single-phase systems and on 3-wire DC circuits

•With line-to-line loads in 3-phase, 4-wire systems and 2-phase, 5-wire systems


In light of the fact that handle ties don't provide for common trip and the fact that the fundamental requirement is for common trip, it seems most reasonable to apply only circuit breakers with common trip in the second and third items above, where line-to-line loads are served. That means eliminating those two items as exceptions.

The National Electrical Manufacturers Association (NEMA) has proposed eliminating these two items from the NEC, and the Code Making Panel is considering it. Acceptance of that proposal will require the installation of common trip circuit breakers in circuits serving line-to-line loads and require that all poles clear the circuit simultaneously.
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