Mains protection query

[dmccombe7]

10 hours ago, skidder652003 said:

Guess we've been lucky then, 100W valve Marshall, 300W D class Markbass Combo, 4 x 400W RCF 15"s, 1 x 800W Mackie 18" sub, numerous lights, moving heads, smoke machine. Not a happy bunny when it's all we're offered TBH, but as I said so far we've been lucky. Does running off several wall sockets help? I mean aren't they all connected to the same ring?

From memory a ring main will typically have a 32A circuit breaker and the load on the sockets will be shared evenly around the ring. When you use everything from one socket the limiting factor is the 13A fuse in the wall plug. 

Dave

[dmccombe7]

9 minutes ago, Steve Browning said:

Minor derail but kind of relevant to the discussion as it's evolved.

 

If a Mesa TT-800 states it's rated at 250 watts (consumption) then the amps being drawn will be 250/230x1.4 = 1.5 amps. Is that correctly worked out? Just trying to get a feeling for the total draw of the band and the number of sockets required.

 

Does it also mean that that is with the thing running flat out? I run mine at about 3 and that's truckloads. I guess that begs the question, does running at 30% (approx) consume 0.45amps?

what's the x1.4 Steve ?

 

I've always looked at it as for every 250W power load its 1A. 

[Steve Browning]

20 minutes ago, dmccombe7 said:

what's the x1.4 Steve ?

 

I've always looked at it as for every 250W power load its 1A. 

I'm trying to find the link. I had a recollection that the square root of 2 had some significance but I'll be Jeremy Thorped if I can see it now.

[Steve Browning]

6 minutes ago, Steve Browning said:

I'm trying to find the link. I had a recollection that the square root of 2 had some significance but I'll be Jeremy Thorped if I can see it now.

Yup. Rubbish it appears.

 

Amps equals watts/volts so my TT is 250/230 = 1.2. They seem to view the UK as 230V for the calculation.

[Mottlefeeder]

There may be some confusion here between amplifier ratings, current drawn on start-up and current drawn in use.

 

An amplifier rated as 100W output will deliver much less most of the time - an average power of about 1/8 of the peak power is possible for bass guitar, and the peak power here will be 100W.

 

To deliver that 12W average power, the amplifier may draw 100W if class A, 48W if class AB (25% efficiency at low power), or 13W if class D  (90% efficiency most of the time)

 

During switch on, a large transformer can draw *6 of its rated current in the initial fraction of a second, and a switched mode power supply can be worse, or can be designed to have a slow start to limit the inrush.

 

When you connect several bits of kit to a single socket, you should switch them on in sequence so that the switch-on current pulse does not take out the fuse.

 

It is unlikely that your class AB amps and class D amps will draw more than 13 A, but your lights might.

 

David

Edited August 10, 2021 by Mottlefeeder
Clarity

[dmccombe7]

40 minutes ago, Steve Browning said:

Yup. Rubbish it appears.

 

Amps equals watts/volts so my TT is 250/230 = 1.2. They seem to view the UK as 230V for the calculation.

We used to be 240V with EU being 220V so it was agreed to go to 230V to standardise AFAIK.

 

Dave

[jrixn1]

If you ever use one of those reel power extensions, bear in mind that they have different ratings for wound and unwound.  When wound, I think it drops considerably (this one drops from 2400W to 720W, so that's just 3A).  We didn't unwind fully once, and it started smoking during the set!

 

 

[Phil Starr]

Ha ha I shouldn't have gone to the gym, now it's got complicated, but everything people are saying is about right.

 

mains in this country (UK) and across the EU is 230V nominally, but that varies depending upon where you are along the power line. Our house averages at 242V. So theoretically 230w is 1A but the general calculation that 250W is 1A is good enough. There's two considerations here; you don't want to trip the fuse and you don't want to set the internal wiring alight! Most household fuses are slow blow to avoid them going every time we turn something on, most stuff in a house takes less power as it warms up.

 

Steve browning has asked the crucial question, what is my amp using when it is on 3?  That's amazingly tricky to work out. If you are damping your strings properly there's a lot of time you aren't putting out any sound, all your notes start loud and then decay etc. The 300W or whatever are simply the top limit you hope to never get near. Then again the amp isn't 100% efficient. Switch mode power supplies are better than transformers, transistors better than valves. Modern electrical appliances now have to have an estimate of average power, have a look on the back of your amp if it is recent. My 500W Peavey says 160Wh electrical consumption so that's an average of 160/230 of an amp when it is run quite hard, about 1/3 of the 500W max output.

 

The next issue is the inflated watts that are advertised, for calculating currents you need good old RMS watts (that's where the square root of two comes in, RMS=root mean square) Most single speakers only handle 300W as a rule of thumb so that 1000W Yamaha PA speaker is actually only 500W at best and needs less than 200W of electricity an hour.

 

SO

add up all the watts of all your amps/lights and so on and allow 4amps for every 1000W. If you are using solid state amps class D or otherwise and LED lighting then I really doubt most pub bands will be using more than 3000W. You don't need a lot of headroom, as in my Peavey I doubt you'll be running at more than 30% for anything longer than a few microseconds. You only need a second socket if you go over 3000W and that gives you a big safety margin. If i have to go for a second socket I look for a twin socket. In a double socket the two sockets are connected by big copper/brass strips so they are properly earthed to each other by design. I don't trust electricians I haven't met as I've worked on building sites. Most are safety conscious but people make mistakes. If I have to split then I run one circuit for the amps and a separate one for lights and make sure no-one can touch the lights. Your mics are earthed through the PA so you need that plugged into the same earth as the back line.

 

The final thing is to make sure your mains leads are in good condition. There's no point in trusting a single socket if anything you bring in has a broken earth. That's where a circuit tester will help, and use the RCD on your single socket if you think there isn't one elsewhere, though most venues will have regular checks for insurance purposes.

Edited August 10, 2021 by Phil Starr

[dmccombe7]

Excellent reply @Phil Starr

That helped a lot.

Dave