Arc-Fault Interuptor Breakers

I'm finishing the construction of a master bedroom add-on to our home.
All the plugs in the room are on a single circuit on a 15-amp arc fault
breaker. Everything appears functional, but during cleanup, whenever I
connect my 7 AMP shop vac to the circuit, it kicks the breaker.
I noticed a similar occurance with a 20 GFI breaker when I attempted to
run an air compressor from it.
I have no problem with either power tool when running them from a
straight 20 AMP circuit.
What's happening here? Are protection breakers just that much more
sensitive?
TIA
Randell Tarin
Reply to
Randell Tarin
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It is probable that your appliances have universal (AC-DC) motors with brushes, thus producing sparks and all sorts of voltage transients on the line. This is what the arc-fault detectors are designed to detect
I guess this means I can no longer run my Tesla coil in my bedroom... Bummer. :>
Beachcomber
Reply to
Beachcomber
What about vacuum cleaners and hair dryers, both appliances typically used in a bedroom? Well, I do have a 100 ft. extention cord...
Reply to
Randell Tarin
A GFCI trip suggests the air compressor has hot-to-ground leakage.
Brush motors are not supposed to trip AFCIs. AFCIs almost always include a 30 mA ground fault trip (GFCIs use 5 mA). It is possible the shop vac has hot-to-ground leakage. If you plug the shop vac into the GFCI does it trip? Do you have more than 1 AFCI - trip the others also?
-- bud--
Reply to
Bud--
| A GFCI trip suggests the air compressor has hot-to-ground leakage.
Or it could have neutral to ground leakage. If the neutral and ground are connected together at the load, the return current will split between those wires, and the GFCI will not see the same current level between hot and neutral. In either case, the compressor is defective and dangerous for use. It needs to be repaired or replaced.
| Brush motors are not supposed to trip AFCIs. AFCIs almost always include | a 30 mA ground fault trip (GFCIs use 5 mA). It is possible the shop vac | has hot-to-ground leakage. If you plug the shop vac into the GFCI does | it trip? Do you have more than 1 AFCI - trip the others also?
There is a history of some AFCIs being overly sensitive, or some motor loads having excess brush arcing, and tripping AFCIs (and not GFCIs). The OP should test the shop vac on a GFCI. If it is OK on a GFCI, then the AFCI should be returned to the manufacturer for evaluation (but they will likely also need more information to reproduce the problem, if not the actual shop vac). And the shop vac could be defective and have a kind of fault, or excessive arcing, that the AFCI should detect.
Reply to
phil-news-nospam
Most AFCI trips get traced back to ground/neutral faults. That is where the ceiling fans got that bad reputation. It was usually that big cludge wirenut vibrating into the hickey when the fan was running. The original AFCI designs (for the arc fault part) were only looking for short duration current spikes in the 70a+ range. They just detect dead shorts from line to neutral. The GFCI protection was added to find shorts from neutral or line to ground at the 30ma level.
Reply to
gfretwell
It's very likely the fault of the shop-vac. I ran the vacuum and a hair dryer without incident. It's on it's last leg and ready for replacement anyway.
Thanks guys.
Reply to
Randell Tarin
| |>|> |>| A GFCI trip suggests the air compressor has hot-to-ground leakage. |> |>Or it could have neutral to ground leakage. If the neutral and ground |>are connected together at the load, the return current will split between |>those wires, and the GFCI will not see the same current level between hot |>and neutral. In either case, the compressor is defective and dangerous |>for use. It needs to be repaired or replaced. |> |> |>| Brush motors are not supposed to trip AFCIs. AFCIs almost always include |>| a 30 mA ground fault trip (GFCIs use 5 mA). It is possible the shop vac |>| has hot-to-ground leakage. If you plug the shop vac into the GFCI does |>| it trip? Do you have more than 1 AFCI - trip the others also? |> |>There is a history of some AFCIs being overly sensitive, or some motor |>loads having excess brush arcing, and tripping AFCIs (and not GFCIs). |>The OP should test the shop vac on a GFCI. If it is OK on a GFCI, then |>the AFCI should be returned to the manufacturer for evaluation (but they |>will likely also need more information to reproduce the problem, if not |>the actual shop vac). And the shop vac could be defective and have a |>kind of fault, or excessive arcing, that the AFCI should detect. | | | Most AFCI trips get traced back to ground/neutral faults. That is | where the ceiling fans got that bad reputation. It was usually that | big cludge wirenut vibrating into the hickey when the fan was running. | The original AFCI designs (for the arc fault part) were only looking | for short duration current spikes in the 70a+ range. They just detect | dead shorts from line to neutral. The GFCI protection was added to | find shorts from neutral or line to ground at the 30ma level.
That's not what some aspects of what I read say. There have been documents (I didn't keep them handy) that described "series arcs" as arcs due to a loose connection that isn't a short circuit path. The arc transients would therefore have no more increase than what the load is, plus or minus any circuit/load reactive components affecting it.
Reply to
phil-news-nospam
There are not any "series arc" detectors out there yet., Siemens is bragging about having one but it isn't really for sale. The "combination" AFCI refers to being able to detect parallel arcs in the wall plus an arc in a line cord. It is a lower level of current detection when looking at a potential arc.
Reply to
gfretwell
A interesting source of information on AFCIs is:
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IAEI News, January/February 2003,The Truth About AFCIs (Part 1) (part 2 is at)
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a response to reader comments)
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The currently required "Branch/feeder" AFCIs are required to detect 75A arcs. That will detect parallel arcs, but not series arcs.
"Outlet circuit" AFCIs are required to detect 5A arcs, which will detect series and parallel arcs.
The "Combination" AFCIs required by the NEC on 1-1-08 combine "Outlet circuit" and "Branch/feeder" requirements, so they will detect both series and parallel arcs (if the AFCIs ever appear).
Detecting a 5A 'bad' arc while ignoring an acceptable arc, like a brush motor, does not sound easy.
The ground fault detection level required in AFCIs is 5A. The article says AFCIs on the market detect at 50mA. The ones I have seen are at 30mA. I believe the theory is that an arc with a ground present is likely to soon arc to ground and be detected.
Among the information in the article is where the 5 and 75A levels came from.
-- bud--
Reply to
Bud--
I think the whole idea of AFCI's and their adoption by the US Electrical Code and Consumer Safety Organizations was because, there were, at most, one or two deaths per year caused by fires started in bedrooms caused by bedframes smashing into plugs/outlets. Americans in general, and the keepers of the NEC specifically like to error on the side of caution, especially if the economic cost is not too high. Also, just the fact that a plug/outlet was located behind the bed would increase the risk of fire.
That being said, most of the electrical devices used in bedrooms are going to be two wire devices, (lamps, electric space heaters, clocks, vacuum cleaners, radios, cell phone/cordless phone chargers, etc.)
Three wire arc-fault detection would be normally not add any greater protection for most applianced used in this location.
Thus, any fault to ground, even an arc-fault could conceivably be protected by conventional, less-expensive GFCI's (although not currenlty required in bedrooms).
Reply to
Beachcomber
| |>| Most AFCI trips get traced back to ground/neutral faults. That is |>| where the ceiling fans got that bad reputation. It was usually that |>| big cludge wirenut vibrating into the hickey when the fan was running. |>| The original AFCI designs (for the arc fault part) were only looking |>| for short duration current spikes in the 70a+ range. They just detect |>| dead shorts from line to neutral. The GFCI protection was added to |>| find shorts from neutral or line to ground at the 30ma level. |> |>That's not what some aspects of what I read say. There have been documents |>(I didn't keep them handy) that described "series arcs" as arcs due to a |>loose connection that isn't a short circuit path. The arc transients would |>therefore have no more increase than what the load is, plus or minus any |>circuit/load reactive components affecting it. |> |>-- | | There are not any "series arc" detectors out there yet., Siemens is | bragging about having one but it isn't really for sale. | The "combination" AFCI refers to being able to detect parallel arcs in | the wall plus an arc in a line cord. It is a lower level of current | detection when looking at a potential arc.
What is the difference between those kinds of arcs that would require a combination device to detect either?
So if I take a power cord with a plug on one end, and open stranded wire on the other end, plug the plug into a 120V output, and take the open ends (held by the insulation), and just quickly slap them across each other and back apart again (with eyes turned away), if a magnetic trip doesn't open on that (and I suspect it won't ... don't try this at home), would an AFCI catch it and open when a magnetic trip won't?
Reply to
phil-news-nospam
| The currently required "Branch/feeder" AFCIs are required to detect 75A | arcs. That will detect parallel arcs, but not series arcs.
What about a 3/4 HP garbage disposal motor starting up against a drain jammed tight with the dinner waste?
| "Outlet circuit" AFCIs are required to detect 5A arcs, which will detect | series and parallel arcs. | | The "Combination" AFCIs required by the NEC on 1-1-08 combine "Outlet | circuit" and "Branch/feeder" requirements, so they will detect both | series and parallel arcs (if the AFCIs ever appear).
So the NEC require in less than a year (where AHJs adopt it all) a product that still hasn't shown up on the market?
Reply to
phil-news-nospam
| I think the whole idea of AFCI's and their adoption by the US | Electrical Code and Consumer Safety Organizations was because, there | were, at most, one or two deaths per year caused by fires started in | bedrooms caused by bedframes smashing into plugs/outlets. Americans | in general, and the keepers of the NEC specifically like to error on | the side of caution, especially if the economic cost is not too high. | Also, just the fact that a plug/outlet was located behind the bed | would increase the risk of fire.
It would also help to require sufficient extra outlets in bedrooms so that the ones that do get covered up by furniture won't matter because at least one other nearby will be available. How about a duplex every 2 feet?
In my current home (I didn't design), I have 3 outlets, 2 of which are in bedrooms, with "permanent" extension cords because they are located where the only option for furniture exists, and another outlet is too far away. The builder clearly put the absolute minimum in to meet code. It would now be very expensive to stick in new ones to meet my suggested spacing.
Reply to
phil-news-nospam
This is a design issue. If the designer can identify the likely bed locations they can place the outlets properly for the night stands. In my bedroom remodel this ended up being 4 quads and two 4 way switch loops with switches at 3 locations for the overhead and one switched receptacle in each quad. Most builders hitting a price point will not do this. In the quads that ended up being away from the bed location I swapped a duples for one of those green nightlights.
Reply to
gfretwell
The difference is available fault current. You may never generate the 75a on the end of an 18ga lamp cord, particularly if it was connected in a flaky 43 cent receptacle with loose contacts.
Reply to
gfretwell
It is a simple overload, not an arc. The arc fault mechanism wouldn't detect it. But the normal overload mechanism of a branch/feeder circuit breaker would.
Yup.
The 1-1-08 requirement is in the 2002 NEC (like post dating a check). It may have been reasonable to expect the new AFCIs would be on the market when they wrote the 2002 code.
What IMHO was a irresponsible move was requiring in the 2008 NEC (assuming it hasn't been removed late in the code process) that almost all 15 & 20A 120V residential circuits be protected by AFCIs. These will have to be the new AFCIs that were not on the market when they wrote the 2008 code. It was likely the new devices would have little field experience before they were required 'everywhere'.
It will be interesting what changes jurisdictions make when they accept the 2008 NEC. If, for example, SquareD does not have the new AFCIs available does that mean you can't use SquareD panels.
-- bud--
Reply to
Bud--
They actually put AFCIs in the 99 code to be implimented in 2002 and that device did not really exist in retail channels in 1997 when the ROP came out.
Reply to
gfretwell
I have never seen bedframes hitting plugs as a cause behind AFCIs. Electrical cords lying on the floor that get walked on, under rugs, or otherwise abused have been mentioned. There was an economic analysis done by the CPSC. It was based on the number of electrical fires with bedrooms a major point of origin. According to the analysis, AFCIs were cost-effective in preventing fire damage, injury and death. The analysis may be right or wrong, but there was a justification for AFCIs in bedrooms.
But I don?t think there was any study that demonstrated the effectiveness of AFCIs that have been installed in bedrooms that was used as a basis for extending the use of AFCIs ?everywhere?.
Two wire cord s produce parallel faults, which is what the existing AFCIs are required to detect. One of the UL AFCI tests is for parallel arcs in ?zip? cord, which is the common electrical cord in bedrooms. The 75A parallel arc detection level is based on UL field tests of outlets that found 75A was available for a fault at all tested outlets and at the end of almost all plugged in lengths of 6 feet of #18.
One of the UL AFCI tests is for a series arc in Romex with ground. Since existing AFCIs don?t detect series arcs I presume detection is by the series arc becoming at least partially a ground fault which will be detected.
Also UL did some tests on ?glowing connections? - series arcs - at wire connections to receptacles. In 9 of 16 tests leakage to ground developed that tripped an AFCI. (In 6 of 16 tests the wire burned open.)
But that wouldn?t detect parallel arcs that don?t involve ground. Or, if the new AFCIs ever appear, series arcs that don?t involve ground. And an arc fault with a ground present does not necessarily develop ground leakage.
-- bud--
Reply to
Bud--
The study I saw at Electrical Contractor Network forum pegged the price at several million dollars per fire prevented and a couple billion dollars per life saved. (using NFPA fire data and industry projections of AFCIs to be sold at $40 each.)
Reply to
gfretwell

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