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#1
Old 06-10-2010, 01:41 PM
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Daisy chaining power strips

While reading this thread I got to wondering how many power strips it's reasonably safe to chain together. I realize that under strict OSHA conditions, the maximum number that could be safely chained is zero, but I'm talking about in a practical non-professional capacity. What would be the real danger of chaining together 4 - 5 power strips, assuming they're all high-quality and identically rated?
#2
Old 06-10-2010, 01:52 PM
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It's about multiplying the potential loads.

So the answer is it depends on the things you hook up to them. For the purposes of argument, we will assume that all the connections are solid.

If you have 4 strips together, A, B, C and D, each one with 4 outlets on it, then you get 3 outlets for use and 1 to continue the chain (with 4 on D since it stops there).

If you plug in 4 things to D then its cord supports the load of those devices. If you plug three things into C then its cord supports those three things *and* the current for D. By the time you get to cord A, at the start of the chain its cord is carrying the load of all of the devices further along.

This is where it gets dangerous, since you can quickly exceed the current rating for the cord (or the outlet iself), and excessive current heats up the wires, melts the plastic and then it can short out and catch fire.

If all the things you connect up are very low power (like cellphone chargers, a laptop charger, VCR, DVD player etc) then you cut the risk of overdoing the current considerably, but they do add up.

Higher power devices like TVs, amps, computers, heaters, AC units, kettles, vacuum cleaners etc are most certainly not suitable for this sort of daisy chaining.
#3
Old 06-10-2010, 02:09 PM
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Quote:
Originally Posted by DCnDC View Post
While reading this thread I got to wondering how many power strips it's reasonably safe to chain together. I realize that under strict OSHA conditions, the maximum number that could be safely chained is zero, but I'm talking about in a practical non-professional capacity. What would be the real danger of chaining together 4 - 5 power strips, assuming they're all high-quality and identically rated?
Honestly -

Just for kicks, open one up some time. Even a "High Quality" one. They aren't. Most typical power strips have relatively small wire, soldered from plug to plug for the hot and the neutral and sometimes the ground. Also, for each strip, you are generally going through a cheap breaker and a cheap switch, each of which have junction resistance.

If you really need to extend the length of a power strip, use a single, decent, grounded extension cord. If you need extra outlets, use a power strip with more outlets.

-- BUT --
It is possible, and mostly safe to daisy chain them, as long as you can be sure that the loads will be small, say, for wall-wart power supplies as an example. The trouble will begin though when you add higher power loads to the last one in the chain, or someone plugs in a vacuum cleaner or power tool...

YMMV
#4
Old 06-10-2010, 02:15 PM
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Right. Thirteen small 120VAC loads might, all together, still be within the ratings of the power strips and the house circuit. Conversely, two large loads might be too much.

If the house circuit is overloaded, you should see a circuit breaker trip or a fuse burn. Some power strips have their own overcurrent devices.

You could daisy-chain a hundred power strips together if you weren't plugging anything into them.

The electrician's answer is, just get one good power strip with sufficient outlets for whatever assembly of components you're using in that spot.
#5
Old 06-10-2010, 02:39 PM
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Just don't do this.
#6
Old 06-10-2010, 02:44 PM
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Originally Posted by Morbo View Post
Just don't do this.
OMG! Are those guys still alive?
#7
Old 06-10-2010, 02:53 PM
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Originally Posted by Morbo View Post
Just don't do this.
Nice. I'm sure they thought they were brilliant.
#8
Old 06-10-2010, 02:55 PM
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A comment there claims that was a "setup"--that nobody was really doing that with live wires.

I think it may have been copied from a real item (involving a floating dish detergent bottle with a duplex receptacle cut into it) from a few years ago in EC&M's "What's Wrong Here?" feature on code violations. I couldn't see a way to quickly find that older picture, but you can see the feature here. Not all violations are as, uh, good as the pool contraptions.
#9
Old 06-10-2010, 05:12 PM
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Quote:
Originally Posted by Khendrask View Post
If you really need to extend the length of a power strip, use a single, decent, grounded extension cord. If you need extra outlets, use a power strip with more outlets.

-- BUT --
It is possible, and mostly safe to daisy chain them, as long as you can be sure that the loads will be small, say, for wall-wart power supplies as an example. The trouble will begin though when you add higher power loads to the last one in the chain, or someone plugs in a vacuum cleaner or power tool...
Well, the problem is I can't find any decent cord in the normal electronic shops I go to. The standard length is 1.2 m (4 ft.), more expensive is 1.5 (5 ft) and very very expensive is 1.8 (6 ft). The next step is a cable drum, which I don't need and which also has issues.

So what I do is daisy-chain two or three together to get to the point in the room where things are plugged in, and only use the one at the end (B or C).

Also, most times I need an extension cord for low-power things like adapters for phone and modem, that have to be on all the time. Otherwise, like plugging in a lamp, or turning on my PC, I bought the more expensive PC-safe power strips (that have spike adapters) and tested very carefully the first time for warmth. Since they didn't feel warm the first time, I assume they can carry the load. (Of course, I have also breakers in my house - who doesn't?)
#10
Old 06-10-2010, 06:04 PM
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Quote:
Originally Posted by constanze View Post
(Of course, I have also breakers in my house - who doesn't?)
Unless they are AFCI breakers they won't do didley for you in this case.

Your standard over-current breakers only trip when too much current for the entire circuit flows through them, typically 15 or 20 amps depending on the breaker and wiring.

A 16 gauge extension cord is only good to about 10 amps. The cord will melt and burn before the breaker trips. Likewise, a poor connection in any of the power strips could easily catch fire with much less than 15 amps going through them.

An AFCI (Arc Fault Circuit Interrupter) trips (shuts off the power) when it detects an arc, like what you get when you have a frayed extension cord or a bad connection in a power strip. AFCIs have been required by the National Electric Code in the U.S. for the last decade or so. They aren't perfect, but they are pretty darn good for helping to prevent fire. You might want to invest in some for your home if you don't already have them.

A GFCI (Ground Fault Circuit Interrupter) measures the current through the hot and neutral wires. If they aren't equal, the GFCI assumes that the current has found some other path to ground and trips. Since the other path through ground is often through a person, this is a good protective device to stop you from getting electrocuted. They are required in places like bathrooms where a person can easily provide an electrical path from a faulty device to electrical ground (via the faucet, sink, tub, shower head, etc).

In summary:
Breaker - protects your house wiring, not so good at protecting you or preventing fires except in major short circuits
GFCI - helps prevent you from getting electrocuted
AFCI - helps prevent fires

Also, if you have to run extension cords everywhere for phones, modems, etc. you might want to consider having an electrician come in and add a few outlets. It sounds like you need them.
#11
Old 06-10-2010, 08:24 PM
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One danger comes from multiplying the number of points of failure. Connections are more likely to fail than wires, each power strip may have multiple internal connections. So you are increasing the failure rate with each daisy in the chain more than just adding an extension cord.
Another danger is the temptation to overload the line because all the outlets are available. You start out just using a few them without undue load, but theres the free outlet and what could it hurt to plug in one more device? Eventually it looks like the picture in the fire safety handbook with a big red X over it.
Another problem, not exactly a danger, is that you increase your chances of accidently switching off or disconnecting a lot of devices at once.

Even electricians may stick to simple, problem free rules, like this one:

Simple rule for when to use copper wiring and when to use aluminum wiring:
Use copper
#12
Old 06-10-2010, 10:02 PM
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Could someone put in somewhat rational order the load requirements of typical components, ranging from comp speakers, the main box powered external drives, phones, etc? I have 3 daisied, all full, all supposedly grounded and circuit-breakered. Have I been living on borrowed time?
#13
Old 06-25-2010, 03:02 PM
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Originally Posted by engineer_comp_geek View Post
Unless they are AFCI breakers they won't do didley for you in this case.

Your standard over-current breakers only trip when too much current for the entire circuit flows through them, typically 15 or 20 amps depending on the breaker and wiring.

A 16 gauge extension cord is only good to about 10 amps. The cord will melt and burn before the breaker trips. Likewise, a poor connection in any of the power strips could easily catch fire with much less than 15 amps going through them.

An AFCI (Arc Fault Circuit Interrupter) trips (shuts off the power) when it detects an arc, like what you get when you have a frayed extension cord or a bad connection in a power strip. AFCIs have been required by the National Electric Code in the U.S. for the last decade or so. They aren't perfect, but they are pretty darn good for helping to prevent fire. You might want to invest in some for your home if you don't already have them.

A GFCI (Ground Fault Circuit Interrupter) measures the current through the hot and neutral wires. If they aren't equal, the GFCI assumes that the current has found some other path to ground and trips. Since the other path through ground is often through a person, this is a good protective device to stop you from getting electrocuted. They are required in places like bathrooms where a person can easily provide an electrical path from a faulty device to electrical ground (via the faucet, sink, tub, shower head, etc).

In summary:
Breaker - protects your house wiring, not so good at protecting you or preventing fires except in major short circuits
GFCI - helps prevent you from getting electrocuted
AFCI - helps prevent fires
Sorry, I was using breakers in the colloquial sense. I'm not an electrician, and I didn't know the correct terms in English. Even with your detailed explanation, I would have a hard time mapping the German technical terms to them. I know that my oven has its own special breaker, because it uses a lot of power, and maybe a different ampage. I also know that my bathroom has its own breaker - it's a different grey box. I assume that the electricians wired all this correctly because there are standards (DIN and building safety codes) which are inspected afterwards. But as layperson, I don't know details.

Quote:
Also, if you have to run extension cords everywhere for phones, modems, etc. you might want to consider having an electrician come in and add a few outlets. It sounds like you need them.
I live in a rented flat built in the 50s, when people needed two outlets for lamps, and a third one for the radio. Putting in more outlets would have cost a lot of money, and nobody could have foreseen people owning a TV, DVD, radio, PC, monitor, modem, answering machine, phone... and a reading lamp today.

Since it's rented, I can't call the electrician, and naturally my landlord doesn't give a shit (a big apt. block owned by a company. )
#14
Old 06-25-2010, 03:09 PM
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Quote:
Originally Posted by Leo Bloom View Post
Could someone put in somewhat rational order the load requirements of typical components, ranging from comp speakers, the main box powered external drives, phones, etc? I have 3 daisied, all full, all supposedly grounded and circuit-breakered. Have I been living on borrowed time?
Most small devices, powered by "wall wart" power supplies draw negligible power - usually under 20W.
LCD Monitors take between 50W-150W.
A big desktop computer can draw as much as 1000W, but most only use around 200W.

Get one of these if you want to know for certain: Kill-A-Watt

Last edited by beowulff; 06-25-2010 at 03:09 PM.
#15
Old 06-25-2010, 03:20 PM
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a GFCI in parts of Europe might be called a residual-current device (RCD)
#16
Old 06-25-2010, 04:37 PM
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Originally Posted by TriPolar View Post
Another problem, not exactly a danger, is that you increase your chances of accidently switching off or disconnecting a lot of devices at once.
Or re-connecting them. Learned that one the hard way after a neighbourhood-wide power outage. When the juice came back on, two computers + 2 screens + a radiator + a big TV + the stereo + a few lamps all came back on all at once in the living room. Boom goes the dynamite breaker.
#17
Old 06-25-2010, 07:51 PM
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Theoretically, you can daisy chain an infinite number of extension cords together safely. However, as mentioned above, it's the load that matters. If the only thing plugged into the previous cord is the next cord, it should be fine.
#18
Old 06-26-2010, 06:13 PM
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Each strip draws as much current as everything plugged into it does. Don't try to draw more current out of any strip than it is rated for. That's all that matters.
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