Not an electrician, need advice re: load on mains power

[diller]

Hi all,

I have no knowledge in your field and would really appreciate some advice.

I am setting up a temporary sound-installation in the corner of a park. There is a school approximately 100m from the installation site. The installation requires 8 powered speakers and a laptop. I am hoping to draw the power for all the equipment from the school (rather than hiring a generator).

I have spent the last couple of hours trying to work out if it is safe to power all the equipment from a single mains socket (using a 100m extension cable).

I understand that the speakers I am using will draw 1.25A each from the mains. Eight speakers = 10A.
The 13" Macbook Pro laptop draws 1.5A (If I understand correctly) giving a total draw of 11.5A.
I understand a UK mains socket can take a load of 13A so it would seem to me everything can be plugged into one socket.

1) Am I going to kill myself and everyone in the surrounding area?
2) Also, is it ok to use a 100m extension lead (or 2x50m)?

Here are the specs for the speakers I shall be using: KV2 Audio - EX6 - The Ultimate Compact Active System

Many thanks in advance for all of your help.

All the best,

Nick

 

[telectrix]

your main problem over that length is going to be volt drop. you'll lose 33V of your 240V using 1.5mm cable extension. also you'd need to be aware of the cable being a trip hazard.

 

[dan86]

100m extension cable. likely issue is volt drop...

 

[dan86]

damn.tel beat me to it. I would have thought you'd be pushed to find a 100m extension tbh.
just had a thought. you're not thinking of joining two 50m extensions together are you..?

 

[diller]

your main problem over that length is going to be volt drop. you'll lose 33V of your 240V using 1.5mm cable extension. also you'd need to be aware of the cable being a trip hazard.

Thanks for the response, telectrix.

Are there alternatives to a 1.5mm cable extension that could preserve the 240v over 100m?

The cable as a trip hazard is not an issue (or rather, it's been dealt with).

 

[diller]

damn.tel beat me to it. I would have thought you'd be pushed to find a 100m extension tbh.
just had a thought. you're not thinking of joining two 50m extensions together are you..?

Thanks dan86.

Ok, it sounds like 2x50m cable is a no no and 100m is unlikely also. Is a generator the best approach therefore and, if so, given the 11.5amps I need to draw, what specs should I be looking for?

 

[telectrix]

for 11.5A you'd need a 3 KVA genny. bear in mind though that the output from a cheap genny is as ragged as a scouse kids trousers.your laptop may not like it.

 

[Lucien Nunes]

I'd use 32A extensions (heavier cable, less drop) with Jumper cables to 13A at both ends. All available from sound/lighting hire sources. RCD protection at supply end essential, other regs to satisfy re earthing etc.

Btw have you any idea how much noise you can make with 10A? Those powered speakers have efficient switched mode amps, unless you're trying to demolish nearby houses I bet you run well below that.

 

[diller]

Thanks to you all for your advice and input. It's been a real help.

It seems my best bet is a 3KVA generator with UPS to prevent surges/peaks from the ragged output for the gen destroying my laptop.

Using a gen also solves my cabling problems as I can conceal it behind a hedge a lot closer to the installation site, reducing cable length drastically.

Yes, Lucien, I will be running the speakers no where near full volume but I prefer to have the extra headroom rather than pushing weaker speakers to max. If I run them at, say, half volume, does that effect the power they require? If so, could I get away with a smaller generator (less than 3KVA)?

Much appreciated,

Nick

 

[Lucien Nunes]

I normally agree with 99% of what Tel says but personally running a laptop on a genny wouldn't worry me much. Cheap gennies produce wonky waveforms and are poorly regulated, but that doesn't matter a whole lot to a laptop because it's just a basic switched-mode supply. I have run all kinds of sensitive laboratory-grade electronics off all kinds of power, and the occasional badly regulated genny / inverter / whatever doesn't seem to be an issue in practice. In fact the amplifiers in the active speakers are more likely to object to poor quality power than the laptop.

About the worst I can recall was that a petrol genny, a top-of-the-range Honda, was left running with the choke on, and was spluttering and coughing and failing to maintain speed. The output was surging and dipping for a while before it eventually cut out, with about £50,000 of electronics running from it via a basic transfer switch that was crashing the whole supply between genny and inverter a few times a second. The damage was one blown fuse. FWIW my own laptop PSU has run from everything from 208V delta power, a 110V DC fairground genny (Yes, DC!) and it did survive being briefly connected to 400V (not by me).

Re. amplifier current, at typical volumes the consumption is likely to be much lower. Sound power is logarithmic - if deafening takes 2kW, very loud will take 200W, loud 20W and fairly loud 2W. But it will depend on the individual active speaker design how much supply current that saves. I've run some very large sound systems off 63A, as in whole artic-loads of speakers, and the needle often sits around a dozen or two amps.

What I'm waffling on about here is that it doesn't sound like much of a problem to provide a suitable supply one way or another.

 

[diller]

Thanks so much, Lucien. It's great to read some first hand experience of similar setups. I read somewhere that Macs are more susceptible to the peaks from a genny so I may use a UPS just for my peace of mind.

Thanks All,
I am way more informed than when I started this thread so the forum has done a great job. Cheers,

Nick