AFCI wattage and fan/light combos

[J976T]

Perhaps someone here can shed some light on 2 AFCI questions that I appear to be getting mixed answers from lighting control manufacturers?

From what I?ve read when dimming a AFCI circuit one should not exceed 1000W as far as the dimmed load ? but my question is when one is using say a lighting control power module (and I guess as well this question applies for general circuits as well) should I still be able to use the remaining wattage for switched loads? I?ve received mixed answers from lighting control manufacturers (not sure if they know the answer or not honestly).

Second question - in instances where one is controlling a fan/light combo on an AFCI breaker ? we need to ensure that the loads are sharing a neutral. In order to do this (in centralized lighting control system applications) the AFCI breaker has to be shared between the lighting module and a fan speed control module. Are there any reliable ?2 pole breakers? that will allow one to maximize the potential wattage output of power modules while at the same time provide a shared neutral (instead of trying to squeeze providing power to 2 modules with one breaker)?

Thanks.

 

[electricmanscott]

I don't know anything about the first part of the question but it seems odd. Who gave you the info regarding the load limitation?

There are two pole combo afcis being manufactured by Siemens. As far as their reliability goes, let us know when you use some.

 

[ELA]

I have read a few articles stating that 1000W Dimmed limitation but they were all pretty old : Ref:
http://www.iaei.org/magazine/?p=3933

See figure E.

I wonder if they are still claiming that is true of newer AFCI units that may have improved over time?

From what they say you can still use the remaining wattage on the AFCI for non dimmed loads.

I would imagine that if 1000W of Dimmed load is an issue for a particular AFCI breaker that I would not want to push my luck by adding additional undimmed wattage to it. In other words, if the AFCI is marginal at 1000W what is to say that it is not even more marginal at 1000W dimmed + 800 undimmed? It would make an interesting test.

I tested a 1000W Dimmer on a Square D AFCI without issue but that is just one one brand of AFCI and one brand of dimmer, and I did not test at 1100 -1800Watts.

 

[kevinkk]

As far as your first question goes the rule of thumb is 60% of the AFCI CB rating when used with dimming loads (total load on CB including non dimmed) this was to help avoid nuisance tripping. When a number of circuits are run next to each other then induce current into near by circuits and can trip the AFCI, keeping it under 60% was in effort to reduce the induction. If you manage your line wires to the dimmer modules you can load the breaker to 80% with out problems and the load wires from the dimmer module to the load are also managed you should not have any problems. I twist the neutral and hot wires together from the breaker to the dimmer module, twist it by hand or order it twisted. I then try to keep the load wire separated as much as possible and avoid bunching them in long runs when using romex.

As far as the two pole breaker goes Siemens makes one that works great (make sure you get the combination AFCI breaker, they are still selling branch AFCI and they suck) the Combination 2 pole AFCI has trip indicators showing which leg caused it.

I regularly install a 42space full of AFCI and feed a few 52 circuit dimmer enclosures with both single and 2pole breakers, and many times split ceiling fan loads between modules and phases with out problems. The only time I have had issues is when using 12/4 romex that is two hots with dedicated neutrals, you must use a two pole AFCI on this run, two singles will not work, also when running more than one circuit in conduit the AFCIs will trip in long runs.

Although it may cost a little more to get rid of any potential nuisance tripping, I run all AFCI runs in 12/2 or 14/2 MC, and then twist all neutral and hot pairs inside the dimming cabinet and panel board. Works great and you can load up the CBs

 

[iwire]

As far as your first question goes the rule of thumb is 60% of the AFCI CB rating when used with dimming loads (total load on CB including non dimmed) this was to help avoid nuisance tripping. When a number of circuits are run next to each other then induce current into near by circuits and can trip the AFCI, keeping it under 60% was in effort to reduce the induction.

Sounds like pure voodoo, where did you get this 'rule of thumb'.

If you manage your line wires to the dimmer modules you can load the breaker to 80% with out problems and the load wires from the dimmer module to the load are also managed you should not have any problems. I twist the neutral and hot wires together from the breaker to the dimmer module, twist it by hand or order it twisted. I then try to keep the load wire separated as much as possible and avoid bunching them in long runs when using romex.

Induction is not what is going on.

Where did you get this info?

I regularly install a 42space full of AFCI and feed a few 52 circuit dimmer enclosures with both single and 2pole breakers, and many times split ceiling fan loads between modules and phases with out problems. The only time I have had issues is when using 12/4 romex that is two hots with dedicated neutrals, you must use a two pole AFCI on this run, two singles will not work, also when running more than one circuit in conduit the AFCIs will trip in long runs.

Why?

Although it may cost a little more to get rid of any potential nuisance tripping, I run all AFCI runs in 12/2 or 14/2 MC, and then twist all neutral and hot pairs inside the dimming cabinet and panel board. Works great and you can load up the CBs

Sounds like more wasted time, where did you get all this info?

 

[ELA]

Sounds like pure voodoo, where did you get this 'rule of thumb'.

Induction is not what is going on.

Where did you get this info?

Why?

Sounds like more wasted time, where did you get all this info?

Bob,
I found his post very informative. It sounded like he has had some experience in practical sense. I would like to hear more.

 

[Sierrasparky]

The twisting of the circuit pairs probably works. I've seen it used in video/Audio facilities.

 

[kevinkk]

Sounds like pure voodoo, where did you get this 'rule of thumb'.

IEEE is the source, most major dimmer manufactures list 1000watt max on their installation instructions. IEEE Published a reference to using 1000watt dimmed load in specifications and listed that a AFCI breaker must withstand the 100amps of peak current generated by the 1000watt dimmed load on startup for a minimum of 5 half-cycles. Also in the published spec IEEE references a 1000Watt dimmed load and how the AFCI should remove DC offset and broadband noise RF used in the logic of the circuit to differentiate between arcs and a normal load. Manufactures of dimmer use the 1000watt limit because IEEE used it in their specification, although if you read the entire specification you will find that the actually load the AFCI can handle is the listed load on the device. But a good rule of thumb would be to follow the Manufacture and IEEE.

Induction is not what is going on.

Where did you get this info?

Induction is what is going on here. AFCI breakers also act like GFCI they look at current leakage. The larger the load on a wire the larger the magnetic field, if you place a conductor in a magnetic field specifically an alternating field a current will be induced in that conductor. When at current is inducted in a conductor of a AFCI protected circuit it will have an additive or subtractive effect on the reference current the AFCI is looking for an if the current difference is over 30-60MA but in some cases 5MA the AFCI will trip.In addition broadband noise can also be induced from adjacent circuits causing trips

Why?

Refer to the above explanation, in romex the individual conductor pairs are not twisted thus permitting induction to parallel pairs, distance increases this.

Sounds like more wasted time, where did you get all this info?

Like I stated it will cost a little more thus take a little more time, but it helps to reduce nuisance trips with twisted pairs and or shielding, but you also get many other benefits with twisted pairs and shielding.
My posts are my personal opinion, based on my personal experience and what I feel to be my quest for better than average work and knowledge. My thought on the NEC is that it is a minimum safety standard and should be every electricians starting point and we as electricians should strive to design build and install systems based not only on the minimum standard but with power quality and increased safety in mind. Some of my posts might be above and beyond the NEC and in some minds a waste of time, understood and noted, appreciate the fact check