Exterior consumer box

[b8c]

I have just completed installation of a consumer box in a barn.
I have run the supply in SWA from a spare MCB in the garage (16A), the consumer box in the barn has a 16A and a 6A MCB.
I want to run lights off the 6a and sockets off the 16A, will the 16Amp mcb be sufficient to power a small band, using keyboard, accordian and microphone? as my reason to run this supply is to have a barn dance.
Any help appreciated
B8C

 

[ColJack]

no idea, ask the band what the wattage of their sound system is..

 

[timtheenchanter]

I would think so.

Athough the "wattage" of their sound system will most likly be more than the actual draw, I doubt (and hope) that they are not running a 4K sound system for rehearsals

I have a 2.5K system for use in theatres, and that will push over 110dB with no problem in a 700 seater hall.

 

[ColJack]

surely whatever wattage they quote for sound has to be less than the electrical draw..? you cannot magically create extra watts from nothing..
power in = power out - losses..

 

[b8c]

thanks guys you are all giving me good advice, but all I want to know is will the 16Amp MCB be ok or do I need to replace it with a 32Amp?
In a hall I'm sure these items would be run off a ring main--?
B8C

 

[rebuke]

It should be fine, as long as you're not running a whole load of stage lighting or similar, however your question makes me wonder if you have the necessary knowledge to be doing this (calling a CU a consumer 'box', talking about just upping an MCB, no mention of RCD protection for the sockets etc)- what size SWA have you installed, have you done all the necessary testing etc?

 

[LiamPope]

surely whatever wattage they quote for sound has to be less than the electrical draw..? you cannot magically create extra watts from nothing..
power in = power out - losses..

But audio equipment 'power' is often quoted in nonsense figures that bear essentially no relation to (and can be more than an order of magnitude higher than) their real power outputs/inputs. That said, if you ask a proper band the rating of their proper equipment, you ought to get a proper answer

Without any real information to go on, it's a bit like asking 'are size 6 shoes OK for a person?'. If the cable installation would allow a 32A breaker, you may aswell fit one. Better over-specced than tripping.

Liam

 

[b8c]

yes to both--- its a MK garage/workshop consumer Unit with RCD fitted fed with 4mm sq SWA over a 20m distance from garage to Barn.
Thanks
B8C

 

[rebuke]

If it's 4mm then you can't go to a 32A breaker - 4mm over that distance (when supplying lighting) would have a max load of just over 7kW, 32A * 230V = 7.4kW, which would need 6mm.

You could go for 20A if you're worried, but as has been said, unless they have some ridiculously overpowered system and turn it up full whack (to the level of generating noise complaints), 16A will be plenty.

What earthing system is in use, and what have you done in terms of earth at the barn?

Edit to add: My calculations were assuming the cable was buried - if it is clipped to a wall or similar then you may just get away with 32A

 

[timtheenchanter]

surely whatever wattage they quote for sound has to be less than the electrical draw..? you cannot magically create extra watts from nothing..
power in = power out - losses..

True, but in an amp, for example a 2x600W output, the actual usable power without distorting is likly to be closer to 2x500W, if the kits properly specced, the power amp should be approx twice the power of the speaker rating so as not to push it too hard and cause clipping (very bad for speakers) so wouldn`t be run at much over 1/2 power.
increase the impedance of the speaker system, and power goes down, ie 2x500w in 4R, quite liklely only 350 in 8R

 

[ColJack]

ah, I get what you're saying now..
yes obviously they don't run the thing flat out.
but at flat out, a 1200W power amp would draw in the region of 1300 - 1500W...
as we don't have the acoustic design of the space, it's impossible for us to tell what percentage of power they would require to run the sound system at so we'd have to work it out on the maximum possible draw and allow for that, or close to it.

 

[sparkyspike]

How big is your barn? And it is open air to any extent? Open air concerts normally require a 8kW PA at least. If you're enclosed then you will need 4kW for, say, 300 people. As barn dance music is generally a much quieter affair than rock music, you will probably only need 2kW, in which case 16A will be fine.

Are you hiring the PA? Have you considered fitting a 16A CEEFORM socket - it may come in handy.

 

[RF Lighting]

Plus, if you are expecting public to attend this event, what provision have you made for emergency lighting, bearing in mind you have an RCD main switch

 

[ban-all-sheds]

but at flat out, a 1200W power amp would draw in the region of 1300 - 1500W...

No, it almost certainly won't, because that "1200W" figure will almost certainly bear no relationship to any sort of watts that a scientist or engineer would recognise, or could measure.

http://www.google.co.uk/search?sour...GGLL_en-GBGB302GB302&q=amplifier+power+rating

 

[ColJack]

BAS.. the quoted figures are from a website that sells power amps..
the specific example was a 1200W amplifier that listed it's current requirements at a number of input voltages..

110V - 12A = 1320W
240V - 6.5A = 1560W