RCDs on my Power Amps

[Kev]

Ok, so I feel foolish asking such a basic question but here goes

I've never used RCD protection on my power amps (currently 2 x Crest pro-lite 7.5). I mainly play venues with standard 13 amp supply (UK) so my basic question is, should I use some form if circuit breaker in my chain and is there any particular model I should look for or is any standard 13amp breaker good enough?

if the answer to the above is 'no' would the answer be different if powering gear from a diesel generator?

 

Thanks and sorry again...

[electronicsuk]

You're using the term RCD and Circuit Breaker interchangeably so it's hard to tell what you're actually asking.

If you want to know whether or not it's worth protecting the supply to your amps with an MCB when they're fed off a 13A plug then no, there's no benefit to doing that.

If the question is specifically about RCDs, the majority of 13A sockets these days will already be protected by an RCD somewhere in the distribution system. Having your own plug-in RCD isn't bad idea for those occasions where the socket isn't already protected, more for the protection of you and the public than that of your amps. You can also test your RCD and be confident that it works, whereas you might not have access to the distribution cabinet where the RCD feeding the 13A sockets is located. 

If you're running from a diesel generator of a decent size supplied by a proper hire co with power distribution then whatever you plug into will already be protected. If you're running off a small stand-alone generator of your own then it may well have a floating earth, in which case an RCD may or may not operate in the event of a fault. 

 

TL;DR: Using a plug-in RCD would have little downside and some potential benefits. 

Edited July 1, 2022 by electronicsuk

[adam2]

Agree, no point in adding an MCB to protect against overload as the 13 amp fuse in the plug will do this.

As regards RCDs to protect against earth leakage, I see little point on a standard mains supply. Many outlets will already have RCD protection, and if you find an outlet without RCD protection, then power amplifiers are very low risk appliances.

High risk appliances are in my view anything involving water and electricity, clothes washer, dishwasher, draught beer cooler, electric kettle, portable water pump, aquarium equipment, ice maker etc.

Or anything normally carried or held whilst in use, power tools, cleaning equipment, hair dryers dryers etc.

Amplifiers are low risk.

A supply from a large generator under competent control should be very similar to a mains supply and similar arguments apply.

In the case of a supply from a small portable generator, then an RCD might be more worthwhile.

[Kev]

Thank you both 🙂

 

[Bazz339]

My small cheap (2Kw) generator does not have  any connection between earth and neutral. Some years ago I carried out an experiment to see whether a plug in RCD would offer any extra protection in conjunction with my RCD tester. It would not trip (And was not faulty) 

 

 

[sleah]

13 hours ago, Bazz339 said:

My small cheap (2Kw) generator does not have  any connection between earth and neutral. Some years ago I carried out an experiment to see whether a plug in RCD would offer any extra protection in conjunction with my RCD tester. It would not trip (And was not faulty) 

 

 

Smaller generators are often 'floating' where there is no reference between their live and neutral terminals and the generator's chassis or true earth.

Therefore the rcd doesn't have any reference to measure leakage.

A floating output could be considered as both 'live' terminals with a potential difference between them, but not to ground.

Useage will determine whether a floating supply or one referenced to ground is best (from a gen as opposed to the grid), I'm not clued-up enough to comment on which is best for what!

[p.k.roberts]

On 7/4/2022 at 12:44 PM, adam2 said:

As regards RCDs to protect against earth leakage, I see little point on a standard mains supply. Many outlets will already have RCD protection, and if you find an outlet without RCD protection, then power amplifiers are very low risk appliances.

Sorry, but I'm going to have to disagree with this. If you're plugging in at a venue, you may well not know whether the supply is fed via an RCD or what condition it is in, so I would always connect my equipment via an RCD. This a very low cost and potentially life-saving device; I can't see why you wouldn't take this precaution. For reference, have a look at BS7909.

With regard to the generator question, there's a useful 'primer' here;

https://electrical.theiet.org/media/1550/operation-of-portable-generators.pdf

[sleah]

29 minutes ago, p.k.roberts said:

Sorry, but I'm going to have to disagree with this. If you're plugging in at a venue, you may well not know whether the supply is fed via an RCD or what condition it is in, so I would always connect my equipment via an RCD. This a very low cost and potentially life-saving device; I can't see why you wouldn't take this precaution. For reference, have a look at BS7909.

With regard to the generator question, there's a useful 'primer' here;

https://electrical.theiet.org/media/1550/operation-of-portable-generators.pdf

I too agree. Amps maybe low risk in an installation, but thrown about on the road they can develop faults as much as any piece of kit. Imagine internal signal cables coming lose and touching exposed mains parts - pretty unlikely, but shouldn't be ruled out.

 

Thanks for the pdf - it fairly well answers my question about floating / non-floating supplies 👍

[Bazz339]

2 hours ago, sleah said:

Smaller generators are often 'floating' where there is no reference between their live and neutral terminals and the generator's chassis or true earth.

Therefore the rcd doesn't have any reference to measure leakage.

A floating output could be considered as both 'live' terminals with a potential difference between them, but not to ground.

Useage will determine whether a floating supply or one referenced to ground is best (from a gen as opposed to the grid), I'm not clued-up enough to comment on which is best for what!

Yes I am aware of that, in the case of my generator, voltage of L1 and L2 with respect to the earth pin of the socket is about 120V, 240V between L1 and L2. My intention was to point out that an RCD may not offer additional protection with small generators. Deeper knowledge and discussion to be had in the Electical and Power sub forum. 

Edited July 5, 2022 by Bazz339

[adam2]

As regards small generators with a floating output and RCDs, my view is that some LIMITED protection IS given by an RCD.

Consider the following possibilities.

1) That the generator output is, and remains truly floating. Under these circumstances either pole of the generator output may be touched with impunity, there is no earth path via the users body and no shock can be received. The RCD will not trip, but it does not "need" to as the person touching one pole of the supply is in no danger.

2) That one pole of the generator output  is accidently earthed, due perhaps to a fault in another appliance or due to a damaged cable. Under these circumstances, touching the now live pole of the intended to be floating supply would be very dangerous. An RCD WILL OPERATE under these conditions. The RCD measures any imbalance between the currents in the two supply wires and WILL TRIP if this exceeds the trip rating of the device.

Current in one wire=2 amps, current in other wire= 1.9 amps, current body of user =0.1 amp. potentially fatal;.

An RCD will detect this 0.1 amp imbalance and trip. Note that the RCD will NOT detect the fault and trip in advance, it relies on the operator getting a brief and hopefully survivable shock and THEN tripping.

Also note that the RCD has to be close to each appliance. An RCD on the generator output will NOT trip in the situation described. An RCD at the supply end of an extension lead will NOT detect and earth fault on the extension lead [tent peg through flex etc.] This FIRST earth fault is not in fact directly dangerous, but if someone then contacts the now live side of the supply, it could kill.

In summary RCDs can give some protection when small generators are used, but you need one per appliance, near each appliance.