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Multiple power strips daisy-chained, code?

Regardless of what you or I think, one suing an inspector would have to overcome his testimony that *he* thinks it is, or can become, dangerous. THAT was the point.

Regarding whether it's begging for an overload or not: If you don't see the expansion of 1 receptacle to 11 via cord and plug connected daisy chained power strips as begging for n overload... well, what can I say. I guess we're not sharing the same common usage of the words. :-) I do note however, that your example below is the installation of 4 duplex receptacles, each connected directly to the branch circuit and housed in a junction box. So the total current drawn is not forced to pass through a single cord and plug.

A completely different setup than 11 receptacles, in two daisy chained power strips are powered through 1 receptacle. Are you aware that the NEC requires that any single load on a branch be limited to no more than 80% of the branch circuit rating? Table 210.21(B)(2) 2005 NEC

The receptacle "sees" the combined load of the 11 receptacles in the strips as a single load. With a single receptacle supplying one UL listed cord and plug connected device, the rating on the device takes care of that. If it is listed for use on a 15A branch circuit, it will be rated at no more than 12 amps. However, when you use a power strip, you can exceed the 12 amps, without tripping either the 15A breaker in the service panel, or the 15A breaker in the strip (if so equipped). For example, one could plug two 7 amp devices into a strip. Using two daisy chained power strips exacerbates the situation.

Using a power strip is a situation that easily allows going beyond the limit specified in the NEC. Daisy chaining makes exceeding the allowable load even easier. That violation can't happen on the bench setup you described, unless the user ignores the ratings on the devices he uses. But it can, and does happen on power strips, even when no single device is beyond the limit.

Ed

Reply to
ehsjr
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But of course, they have to help support the "anointed". OTOH i think you are just a little ways "up the hills" from me on US 50. And having been on multiple sides of the table i have issues with a portion of bureaucrats. Best of all i have my licence and a head full of how. Perhaps we can work something out. You can find me directly if you want to read the whole post.

Reply to
JosephKK

There are ways that can be done.

Yeah. I think we need to talk.

Label it as a disconnect switch and use an appropriately rated switch.

Reply to
JosephKK

Thanks, Joseph. Very kind. Yes, we are a bit up the hill, Cameron Park where the old Sam's Town used to be (the church is right behind it). But first I'll see what the inspector says (the church folks want to talk to him first, then hand it over to me).

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Joerg

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I sure hope so :-)

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Joerg

Almost. Someone had placed a rheostat for a speaker in there. Said on the package that it fits into "standard electrical boxes". So ...

Luckily it was caught when a PVC-like stench wafted through the area.

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Reply to
Joerg

Probably because many circuits are 20A these days and the strips are only rated at 15A. So there has to be something that trips off should

15A be exceeded. For example if someone plugs in a space heater plus a hair dryer.

Well, yeah, but what is the difference whether it is one, two or three strips? IMHO, if you place three strips connected to three different outlets (passes "official" muster) that will exhibit about the same level of risk as placing them in a row (does not pass muster for whatever reason). Provided, of course, that those are all properly rated.

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Joerg

Nope, it sure doesn't. This is one out of a bazillion reasons why not:

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Typically those things are UL-listed.

[...] 
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Joerg

The normal failure mode for a MOV is to start conducting at normal voltages and go into thermal runaway.

If you read hanford.gov "Underwriters Laboratories Standard UL 1449, 2nd Edition, Standard For Safety For Transient Voltage Surge Suppressors, now requires thermal protection in power strips. This protection is provided by a thermal fuse located next to the MOV."

In other words, when a MOV overheats it is disconnected from the circuit.

UL 1449 2nd Edition was effective 1998.

None of w's horror sites say plug-in suppressors that are UL listed and have been made for the last 10 years are a problem. (None of them even say an overheated suppressor had a UL label.)

w believes plug-in suppressors do NOT work. Lacking valid technical arguments he resorts to scare tactics.

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bud--
Reply to
bud--

They can do the same to any outlet and there is no current protection device.

Not quite. You can safely draw more current from three (two) outlets than one. There is also only two sets of contacts in series in the parallel power strip case.

Reply to
krw

However, then the space heater will be in one socket and the hair dryer in the other. With a power strip they'd be in the same socket (where the power strip plugs in).

When the circuit is rated 15A (or the power strips have their own 15A breakers) and the power strips are rated 15A, what would be the problem?

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Joerg

Information from Wiremold is at:

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Aluminum plugmold has an inline switch available (amp rating not given???). (Home Depot is not aluminum plugmold.)

letterman also suggested using plugmold with a cord and plug off the end. Your fire inspector may not like that idea.

There are boxes in the Wiremold information that can be mounted on top of an existing box to feed permanently wired plug mold. A switch could be in the box. Some plugmold has 2 circuits (A-B-A-B). or you could use

2 lengths of plugmold from the box (or 1 length cut in half). Or one length could be split in 2 parts with an extra wire returning from the far section to the supply box. This is all surface mounted wiring.

Permanent receptacles are calculated at 1.5A each (a duplex receptacle is 1.5A). Permanent plugmold is 1.5A per 5 foot length (or 1.5A per 1 ft. length if concurrent "appliances" will be used - your equipment is not likely an "appliance".) Total current to be under branch circuit breaker rating. (This does not apply to residential.)

There 'should' be no problem plugging your outlet strips into permanently wired plugmold. (Might want to ask your friendly fire marshal.)

(Information is consistent with the NEC. Your jurisdiction could vary.)

--
bud--
Reply to
bud--

Thanks, that is an idea. Hard-wired installation might be an issue because this is a "raised-foundation" add-on structure on the floor of the sanctuary. But we'll talk it over with him.

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Joerg

Entirely reasonable logic. But UL does not agree. UL listed equipment with a 15A plug can have ratings well above 12A (and as far as I know, up to 15A). An example might be a hair dryer.

This was one of a number of reasons given to change the NEC in one code cycle. (The code panel response was essentially we are right and UL is wrong. The answer to other reasons was essentially the code is written how we like it.)

Another reason was the NEC 80% rule is generally for "continuous" loads, which are 3 hours or more. This is apparently because most breakers and fuses may trip at less than 100% if loaded for more than 3 hours, probably from accumulated heat in the enclosure.

(Another reason is the restriction applies to what end users do after the inspector is long gone. Enforcement is a bit problematic. This is very uncommon in the NEC.)

Receptacles, both 15A and 20A, are tested by UL at well over their nominal rating. Far as I know plugs and receptacles are UL rated for

100% use (probably another reason that was given to change the code).

But you are right that the NEC has an 80% limit for a single receptacle when there are 2 or more receptacles on the circuit (a duplex receptacle is 2).

Daisy chaining can be a mess. And daisy chaining certainly makes it easier to overload a circuit. But you can easily overload a circuit with a single power strip, which I think was one of Joerg's points.

A 'compromise' (which the fire marshal probably wouldn?t go for) would be for Joerg to furnish amp ratings for what is connected to see if the use is 'reasonable'.

Reply to
bud--

The point is that you can plug in a 20A device into a 15A socket on a 20A circuit and there is no protection.

With two strips in parallel you (safely) can draw 20A on a 20A circuit. In series, only 15A, circuit breaker or not. That's why I said series is "not quite" the same as parallel.

Reply to
krw

load,

If you want to test all the breakers you would want to do it at the panel by temporarily connecting a test load. (Or with a separate breaker tester using high current low voltage so you aren't dumping a lot of heat.)

Looking at trip curves for a SquareD breaker, at 120% of rating the trip could be 50 seconds to never. At 200% of rating trip time could be 8-40 seconds.

--
bud--
Reply to
bud--

A 20A device with a 15A plug would not be UL-comliant.

That's what I keep saying, that I don't really see a safety issue with properly rated series connections of strips.

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Joerg
[...]

It's 3A tops. I am going to suggest that we put a sign right where the strips are (very hard to reach anyhow) not to plug in vacuum cleaners and such. In Englisch and Spanish :-)

[...] 
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Reply to
Joerg

Incompetent inspectors. ;-)

Cheers! Rich

Reply to
Rich Grise

Thanks. I did not know that.

Yes, for branch wiring (210.19) and breaker size (210.20). But there is no mention of continuous load in 210.21, which requires the 80% rule for the receptacles we are discussing.

Yes.

Yes.

Yes.

Aside from whether or not it was a point Joerg made, the three ideas you expressed above are at the heart of the issue.

Ed

Reply to
ehsjr

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