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Opinions on power distro build

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tomr_29 View Drop Down
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    Posted: 28 August 2012 at 1:33pm
I'm in the process of designing / building a proper distro for my amp rack and am just after a few opinions on what's best practice and any suggestions on things that might be useful to include. Prefer to get it right first time than have to go back and modify.
 
I'm going to use a Powercon 32A input, probably on the front, to save space and will not be fitting a 32A link out since I won't need it. Input will be monitored for voltage, current, wattage and power factor.
 
I then want to run 6 x 20A Powercon outputs to supply the amps and a 13A socket strip on the back of the rack, breakered in pairs on 20A Type-C. Then also 4 x 10A IEC breakered on a single 10A Type-B for the LMS / Compressor / Low power things.
 
On the main input I will use a 2-pole 32A Type-C. Will I need to include RCD protection also? I have found a 2-pole MCB with built-in RCD (monitoring live but with a switched neutral) but its circa £90+VAT. Is it worth it?
 
I assume a common neutral (post MCB) is safe to do and won't interfere with PAT testing?
 
Case will be steel (zinc plate) with earth tags front and back, outside primed and sprayed.
 
Suggestions welcome Wink
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shagnasty View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote shagnasty Quote  Post ReplyReply Direct Link To This Post Posted: 28 August 2012 at 5:36pm
I wouldn't bother with the 32A c on the input, no need.
 
I don't know if you have seen this thread :-
 
 
I moved it out of a thread called 32A distro build to focus on the cheap metering options, but it show pretty much what you describe but the 13A strip is connected via a powercon....
 
 
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Max_SPL Quote  Post ReplyReply Direct Link To This Post Posted: 29 August 2012 at 5:31am
Hello Tom

Yes put a 32amp circuit breaker on the input, it is there to protect the internal wiring between the supply and the out going circuits so if a fault occurs between the input and out going you are not relying on a third party for protection.

Something else to consider is the kA rating of the circuit breaker, this is the kiloampher rating, this is the amount fault potential in the circuit before the circuit breaker trips. This information is printed on top of the breaker and it will be rated as either 1kA, 3kA, 6kA, and the ratings keep on going up.

The factors which affect this are what is supplying the distro you are going to build, if for example you will be operating mainly off generator sets then you are going to probably need to consider a higher kA rating.

It is important to consider this because if you plug your distro into a gen set and it has a breaker on it with a 25kA rating and you distro only has breakers of 3kA that means under a fault condition there is an extra 22kA of fault current flowing through you breaker befor it trips for the fault it is protecting , the likely result is it will weld your circuit breaker on and it will not protect your equipment.

If you choose a breaker with a higher kA rating it will not matter if there is a lower rated one before it as this will not affect your system, it is only a problem if it is the other way around.

Hope that makes a bit of sense, if not pm me and I can explain further.

Cheers
Shaun
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dylan-penguinmedia Quote  Post ReplyReply Direct Link To This Post Posted: 29 August 2012 at 8:50am
Something's not right with the above.

The majority of domestic MCBs have a breaking capacity of 6ka. Older Wylex drop in jobbies, 2 or 3 but that is irrelevant. The majority of half decent commercial grade MCBs have a breaking capacity of 10ka.

For a 2u amp rack distro - there is absolutely nobody in their right mind that would say you need a 25ka rated breaker for a 32a incomer. That's barmy. By the time you've got down to your 32a 6mm cable, the breakers would have been sufficiently selected for their position in the chain to offer the protection you need on all levels.

So yeah, put in a 32a DP MCB / RCBO if you like - but just pick a decent commercial 10ka one - don't go hunting for stuff you don't need - because nobody else specs it. Avoid Wylex like the plague.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tomr_29 Quote  Post ReplyReply Direct Link To This Post Posted: 29 August 2012 at 10:05am
Cheers guys. Is it worth the input breaker also having RCD functionality?
 
The meter I have been looking at is a little more expensive but includes PF measurement. Perhaps a bit overkill but I was after a much smaller display.
 
@Shaun. Yeah that makes sense but 25kA seems a lot??? I've chosen Merlin Gerin breakers rated at 10kA (not purchased yet though). I rarely run from a genny but when I do I have in-line RCDs and a breaker panel plugged into the genny to split phases.
 
One thing I am unsure about, however, is load sharing at venues where only 13A sockets are available. I usually power my bass amplifier on a seperate socket from the rest. Is there any way to share the load across 2 sockets SAFELY into a single distro? Otherwise I'd be limiting the power I could draw in some venues to around 3kW RMS and running an amp separate from the distro would kind of defeat the point...
 
Edit: Added make of breakers.


Edited by tomr_29 - 29 August 2012 at 10:07am
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shagnasty View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote shagnasty Quote  Post ReplyReply Direct Link To This Post Posted: 29 August 2012 at 1:02pm
Merlin C60 (10KA) are my weapon of choice but as they have doubled in price and half are now badger Schieder I've started using contactum.
Again you don't need an input breaker, it serves absolutely no purpose and personally if you like the single rcd set-up I'd go for a 100A rcd as apposed to any kinda rcbo on the input.

If you use switch mode amps output rcbos are a better bet than a main rcd as split leakage not compound it.

As for running safely off 2 supplies, yes via a dual fed pure sine wave inverter/ups setup, prob is the likely power factor issues will negate your extra 13a as losses.

Personally I'd run a second lead from the same double socket and plug my biggest amp into that before I used any kind of "widow maker" adapter, truth is a widow make probably doesn't let you pull much more than a single 13a plug.

In the event I've had problems on small gigs my racks have taken the 32 B-curve device not the 13a fuse.

If you want a dual 32a feed option then build 2 distros in one box and fit a change over switch to one input (over a dpdt contactor if you want automatic dual mode selection) just be aware you may need to earth lift one supply under certain circumstances and you will have no load balancing, but you won't kill anyone!

As 25KA rupture current kit on a 32A board? Gotta say "get a grip" I've toured huge systems, like multiple trailers of rig and never seen 25KA gear on amp racks.
The point of a rack distro to break down a safe supply, hence the notion you may need an input breaker is strange, if you have fed if from a 1MVA Cummins PowerBox via 500mm of 240mm cable straight to a 32a breaker and then your distro, yes you may need more than 10kA, but in reality sub distro between you and the feed will drop your PSC a lot.
Just as a reality check, I've never metered more than 2.4KA on the final distro side of a pair of load balanced 250KVA sets.
So you are probably ok for an amp rack at 10KA and I'd leave the air controlled switch gear out of it.....




Edited by shagnasty - 29 August 2012 at 5:17pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Max_SPL Quote  Post ReplyReply Direct Link To This Post Posted: 29 August 2012 at 4:47pm
Sorry guys, 25kA was just an example, I work on a dredging vessel and we have these type of fault currents as there is 27 megawatts of power installed on board, for the number nerds the main engines are Wartsila 2 x 12V46 and 2 main generators at 11500kva

The main reason I mentioned this in the thread earlier is to make people aware of some other factors to consider when choosing equipment.

Buy quality like MG and no probs

Edited by Max_SPL - 29 August 2012 at 4:49pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote shagnasty Quote  Post ReplyReply Direct Link To This Post Posted: 29 August 2012 at 5:15pm
Originally posted by Max_SPL Max_SPL wrote:

Sorry guys, 25kA was just an example, I work on a dredging vessel and we have these type of fault currents as there is 27 megawatts of power installed on board, for the number nerds the main engines are Wartsila 2 x 12V46 and 2 main generators at 11500kva

The main reason I mentioned this in the thread earlier is to make people aware of some other factors to consider when choosing equipment.

Buy quality like MG and no probs
Good for a party then, I am guessing 11Kv so best bring a little tranny!!!LOL
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Max_SPL Quote  Post ReplyReply Direct Link To This Post Posted: 29 August 2012 at 5:30pm
No only 6.6kV and we can step down to 380v or 220 if you like

Sometime when I am back on dry land in need a reality check, I don't usually trust dry land it does not move, if the horizon is not going past every few minutes I start holding onto things because I think we may be sinking

I have some pics of the main engines somewhere will try and find them and post here
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tomr_29 Quote  Post ReplyReply Direct Link To This Post Posted: 31 August 2012 at 2:11pm
Cheers guys. Some useful points. I've come up with a design using two power inputs with independant internal circuitry and then DPDT relays (50A rated) which allow either input to be used to power the whole unit but that then seperate the unit into the two individual sides if powered from both. Each input is monitored independantly. RCDs are not included but I have 2 x 16A in-line RCDs which I always use when running from a genny.
 
Any chance someone could have a glance over the schematic just to check I've covered everything? (PM me)
 
Much appreciated.
 
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