Teory behind Not Daisy-Chaining Power Strips

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wirenut1980

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Plainfield, IN
I understand that daisy chaining together 2 or more power strips/surge protectors is a no-no per a UL Standard and doing so violates 110.3(B) of the NEC. What I am having problems with is understanding the theory behind why that is not allowed. I have heard that you could have circulating ground loops/current between the two strips which would put objectionable current on the EGC. I also have read that you could get voltage drop from putting too many of these things together. Anyone have an opinion? :confused:
 
Re: Teory behind Not Daisy-Chaining Power Strips

I think it is simply an overload issue.

In my opinion, it doesn't violate 110.3(B), because relocatable power taps are beyond the scope of the NEC.
 
Re: Teory behind Not Daisy-Chaining Power Strips

It seems to me no matter how many power strips you daisy chain, they are still protected as well at the end of the chain against overloads as they are at the front of the chain.

I think someone at UL just decided this was the way they were going to list them.
 
Re: Teory behind Not Daisy-Chaining Power Strips

From my understanding when installing a 15a or 20a circuit the size of that circuit is based upon the anticipated load to be served or as the NEC dictates because of where the outlets will be located.
One should never intentionally overload a circuit with the expectation that the OLPD will provide OL protection.
With daisy chaining power strips I would be inclined to expect that there is a very strong potential of overloading the first power strip and depending upon the OLPD in it to provide OL protection. Also, If that string of power strips were served by a 15a outlet it would be subject to overload.
Yes, it is common for power strips to serve a lot of minor electronic loads, i.e. computers, printers, scanners, stereos, etc, but in an office situation a secretary may be apt to plug in a heater because of cold feet.
 
Re: Teory behind Not Daisy-Chaining Power Strips

My point is not that you should overload the branch circuit or the power strip, but that it is quite possible to overload the power strip without plugging another power strip into it. The branch circuit OCPD protects the circuit and the power strip equally well whether you have one power strip by itself or ten daisy chained together.

Look at it this way. Suppose you have a 20A OCPD on your branch circuit. You plug a power strip into the outlet. You plug a couple of electric heaters into the power strip - total current 30A. The power strip and the branch circuit are protected by the 20 A breaker.

Suppose you have a power stirp plugged into the outlet and another power strip plugged into the first power strip. You plug one heater into the first power strip and another into the second powerstrip. Same level of protection as the first case.
 
Re: Teory behind Not Daisy-Chaining Power Strips

And what's the difference between a single strip with 10 receptacles versus two 5 receptacle strips daisy chained?

I think this is some OSHA rule or something, as our Facilities department goes on a rampage every few years in regards to this. Our safety monitors now have that item on their monthly checklist. We also had to get rid of all power strips without a metal housing. A plastic surge strip melted down and caused a small fire, so now we can only buy ones that have a metal outside case.

[ June 10, 2005, 04:29 PM: Message edited by: suemarkp ]
 
Re: Teory behind Not Daisy-Chaining Power Strips

I don't know a lick about UL standards but I would have to think that it is a safety issue dealing with the internal components and the wiring of each strip and people simply connecting random loads on them.

Let's say that we daisy chain four strips rated at 15A each on a 20A circuit, with strip #1 being connected to the circuit or receptacle and #4 being the farthest one away on the chain. People are just going to connect things at random and not care about the total load.

If we randomly put load of 5A on #1, 3A on #2, 5A on #3 and 5A on #4. Each one individually is loaded very lightly and within limits, but #1 will be seeing the current of all four strips, or a total of 18A.....more than strip #1 is able to handle and less than the current protection of the circuit, which won't trip the breaker.
 
Re: Teory behind Not Daisy-Chaining Power Strips

By the way, UL prohibits using an extension cord to feed a plug strip also. :D
 
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