Overloading Extension Cables

[Reddkryten]

Hidey Hi.

This is kind of an odd question, if you don't want to read the whole post, here is the cliffnotes version. How much power can I take from a wall socket before it blows and can I plug one power strip into another power strip?

The reason I ask is I'm building a soft box from the book "Nuts and Bolts Filmmaking" great book, I highly recommend it. There is a picture on this site if you scroll down http://www.cvisual.com/film-books/nuts-and-bolts-filmmaking-table-of-contents.asp
For my one, I'm going to use 4 20watt compact fluorescent lights, so 80watts.

In the book, the guy wires the lights up, but I'm not great at electronics.
So my idea is to use four clip lights http://www.amazon.co.uk/Skytronic-CLIP-ON-LIGHT/dp/B000NVRCM0/ref=sr_1_3?ie=UTF8&s=diytools&qid=1215269362&sr=1-3 and plug them all into a power strip.

Now, I was always told never to plug a power strip, into another power strip. So what happens if I have say two or 3 of these 80w soft boxes and plug them into another extension cable?
Here's an awful diagram.

80w soft box powerstrip
So wallsocket - Powerstrip <
80w soft box powerstrip

Is this safe or am I looking at plans for a bomb?

In the future how can I tell how much is too much to put on a socket? Not to sound ungrateful but I don't want to keep bugging you guys with this question every time I plug in a light. Teach a man to fish yadda yadda.

So, is my soft box safe and how do I work out how much power I can take from a socket?

PS (I'm in the UK, so the maximum wattage might be slightly different, but same principle.)

Thanks in advance for stopping me from blowing myself up.

[ciwi286]

I'm not really sure but I thought I should mention to anyone in a different country that your talking about a 240v socket. (America uses 110v)

[waveform]

For 240V systems:

So long as your extensions are rated at 13 amp, correctly fused, are in good condition, and fully unwound, you should be good to put 2000 watts through them safely. That's my limit anyway, it'll take much more.

Fit an RCD between the wall socket and the extension, good safety device.

You can plug one extension into another, so long as the cummulative power being drawn from the wall socket does not exceed that 2000 watts.

[Reddkryten]

2000watts, yay, I'm happy that I have a number to work with. So I could put 25 of those lights on before blowing it'll blow? (25 lights, 4 20w cfls, outputting the equivalent of 100w of light...10000w. I'd probably go blind before hitting the upper limit.)

BTW are you talking about a normal home use power strip or some kind of special heavy duty DIY shop one?

Thanks waveform.

ciwi286, I knew there was a difference between UK and American voltages, I just never knew the exact numbers, btw I could be wrong but does France use 230v?
Then a wire can have a high wattage, but low voltage, 1000w at 2v, then there is hertz, 50hz, 60hz.
Just trying to fry brains without the aid of electricity.

Thanks.

[waveform]

Yup, normal off the shelf extension cables for domestic use, just check their rating is 13 amp to max the power available, some of the wind-up ones in particular have lower ratings.

Yes, you could have 100 x 20 watt lights safely.

Jerry

[ciwi286]

Things used in Europe are rated for between 220v-240v (at least all my stuff is). Anyway, as long as the powerstrips you use are fused, you should be safe.

[Videopia]

Yea, it's about amps, not watts or volts. Jerry knows more about this than me, I'm sure, but I can tell you from experience:

- I'm running 15-20 23w CFLs on a single circuit with no issues. There's also a laptop, LCD studio monitor and a little audio box on it too. It's a totally unsafe jungle of spaghetti in terms of tripping and falling potential, but power-wise, no problem.

- I've also done completely unsafe things with studio tungsten lights that would freak out a fire marshal and - while I don't recommend this at all - I've always known well before catastrophic failure that something was wrong. Breakers blow. Extension cords get really really unnaturally hot. But I've only ever melted two lights and both times those were Stupidity + Heat issues, and not electrical.

________________
“I find television to be very educating. Every time somebody turns on the set, I go in the other room and read a book.”
-- Groucho Marx
videopia.org (http://videopia.org)

[Skycarl]

Yea, it's about amps, not watts or volts.

Videopia nailed it there. Amps represents the power.
Voltage is the amount of electrons going through a line,
amps are the power to push them, and resistance is the drag
you could say as the power moves. Wattage is the power
consumption of the total. Amps X Volts = Watts

The resistance creates heat so the size of the lines are
important. To small and they heat up too much, too big and you
lose power. That's why it's a good idea to use manufacture
suggested wiring as they have figured all that stuff out.

[jburas]

In America, most fuses are 15 or 20 amps on a 120 volt circuit. So using the power of math:

15 amps x 120 volts = 1800 watts
20 amps x 120 volts = 2400 watts

DON'T GO TO THE MAX because electricity isn't exactly reliable, so your power might dip down at some point and blow a fuse.

Remember that circuits are not just a single electrical outlet. Circuits usually are all of the outlets in an entire room, or even several rooms. Always check your circuit breaker before powering tons of lights.

[Reddkryten]

I'm trying to imagine the cable jungle of 20 + lights. BTW what unsafe things did you do...putting a gel directly onto the light?

Skycarl, so watts / voltage = amps?
80 / 240 = 0.33.? Is that correct or did I use the wrong formula?

jburas, that's kinda interesting about the circuits. I heard that the circuit that powers the oven is the most powerful and was told that was the only place I could plug in a blond (1kw) light, while it was running, nothing else could go on that circuit.

Are their any other circuity tricks I should know?
How do you determine which plugs belong to which circuit. There is a plug socket on the bottom left of this room and another at the top right, how would I test if they are the same? I'm not asking for any reason, but I think that skill could come in handy.

[waveform]

That thing about the cooker socket is nonsense Reddkryten.

A typical UK installation in a modern house will have 32 amp Circuit breakers on the ring mains, and a 32 amp on the cooker. The cooker itself is likely to be around 3000 + watts, hence it has a dedicated feed.

The thing with voltages is that for the same wattage at a lower voltage the current draw is higher, all of that is academic though, keeping the techy stuff out of it, look at your typical plug in fan heater at 2000 watts, a toaster at 1500 watts, and my kitchen kettle is 3000 watts!!

To test whether a socket is on the same circuit as another, simply switch off the circuit breaker for that ring, and plug in something to test for power.

[Reddkryten]

That thing about the cooker socket is nonsense Reddkryten.

I can believe it (that it's nonsense I mean). My directing teacher told everyone that, so basically it's the same as everything else he said.

[waveform]

Well, I'm sorry, but it is simply not right. A 1kw lamp can be plugged into any ring main socket

[Reddkryten]

Thanks for telling me, that'll save me a huge mess of cables coming from the kitchen.

And please, don't be sorry. This kind of error dosn't come as a shock to me :rolleyes:

[Skycarl]

http://www.the12volt.com/ohm/ohmslaw.asp
That page has the big ohms law pie chart. Hope it helps get the formula right.

[Reddkryten]

Okay, going slightly off my own topic, but.

I was always told (not much faith in my teachers at the moment) that a blond light was 1kw. I was reading Nuts and bolts film making (recommending it again) which said a blond was 2kw.

Is this something to do with the American 110v to the UK 240v system? Or was I misinformed?

[Reddkryten]

Hello it's me again.

I ran into a little snafu. I was planning on using four clamp lights, but then I found out I need eight. whoops.

So a power strip is out of the question as it would become too bulky.

Does anyone know of a way of connecting multiple wires together without setting the place on fire or killing myself?

Also is there any way to add an off switch to a power cable? My plan was to just use the master power switch on the power strip, but...

[waveform]

You can get power strips with individual switches: ebay item (http://cgi.ebay.co.uk/4-Gang-Way-2Mtr-13Amp-Indvidually-Switched-Ext-Lead_W0QQitemZ190232564925QQcmdZViewItem?hash=item 190232564925&_trksid=p3286.m14.l1318)

If you used a 6 gang one, and plugged your 4 gang into that, you'll have 9 available switched sockets. Again, I recommend that in total you do not exceed 2kw through this arrangement, but again, if you do it is protected against overload anyway. 6 Way version (http://cgi.ebay.co.uk/6-Gang-Way-2Mtr-13Amp-Indvidually-Switched-Ext-Lead_W0QQitemZ190232565881QQcmdZViewItem?hash=item 190232565881&_trksid=p3286.m14.l1318)

[waveform]

Sorry, just found this, and eight gang one, but not individually switched. 8 Gang (http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=200234628325)

Btw, aren't your clamp lights fitted with in line switches?

[Reddkryten]

Hi.

The 8 gang one is perfect.

Yes the clamp lights have individual switches, but what I'm looking for (and the 8 gang one has) is one switch to cut power to every light in an instant.

I had one idea, what about two standard 4 gang power strips, connected to one of those square 3 way adapter plugs. The only thing is, most of the 3 way plugs I have seen has no off switch, is there anyway to install one along the line?