Running a system from a Generator

[MrSpeedy]

Hi there,

 

Here is the situation:

 

I have been asked to provide disco entertainment in a marquee in a middle of a field.

 

A full sound setup totalling around 3.5K and a lighting setup of around 1K will be used.

 

The client has a generator on the site (although I'm not sure whether or not it is hired, I assume so)

 

I am aware of spikes and surges, regulated supplies etc etc

 

However, how likely is equipment such as amplifiers, speakers, lighting effects and sound consoles going to be damaged?

What is the likelihood of damage being sustained from a standard builders generator (3.5k output) as opposed to a 3 phase regulated big bad generator?

 

Also if anyone can suggest the best generator to use / tips to avoid damage, etc I would be very grateful!

 

Regards,

Toby Reynolds

 

(If this post is in the incorrect place, mods, please feel free to relocate)

Thanks

[csg]

In general terms, avoid unregulated petrol building site gen-sets, and insist on power from a regulated diesel powered unit. Make sure the unit ie earthed correctly, and ensure that your supply is protected properly by a suitable MCD and RCD.

 

In terms of generator size, on the presumption that you are the only person using the set, you will need to use a unit of approx. 10Kw capacity, bearing in mind that most of your unit will present an inductive load in dynamic way- which is difficult for the generator to cope with.

 

To improve the stability of the system, I suggest introducing a resistive component to the system, such as a load lamp or electric heater - something of 1Kw should be adequate.

[Dodgecaliber]

I wouldn't really say your going to get any damage asuming you take the basic steps. Whether it's a genset or a little honda petrol toy, it still generates the same flavour of electricity.

 

 

Just make sure that all your kit/distro is isolated when starting up/powering down and you'll be fine! Something around 10k is needed so you have a little extra room. Rule of the thumb is to go for a diesel as it's a bit better running than a putt putt putt petrol thing.

 

 

Dodge

[MrSpeedy]

Hi guys,

 

thanks for the reply's

 

this is as I expected and will need to pass this info onto the client.

 

Its actually a running event at a farm and the track will be floodlit so I would suppose that would contribute towards the 'static' power draw (heater etc)

 

 

@ CSG, an MCD and RCD? I understand what these are but how will these function with the system, i.e. should I expect the generator to have an rcd protected output or do I need to purchase something RCD protected, if so, what would it be??

 

Thanks

 

Toby

[csg]

Unless you are operating as a production electrician, I would expect to be supplied with a correctly protected electrical supply. In practice, this may not happen, so it might be prudent to bring with you a coupe of 13A in-line rcd units to protect yourself from certain faults.

 

In your occupation, they would prove themselves useful on many occasions I suspect, so it should be money well spent.

 

As to the comment above, regarding petrol generators - personally I would avoid them like the plague, due to their poor regulation, which given your dynamic load will result in variable voltage and frequency, which may well upset or damage your equipment.

[sleah]

Regarding rcd's. If you decide to put your own inline, don't think they will definately save your life :o

If the supply has a 'floating' earth, as with most small petrol generators, the rcds will do diddly squat, as they won't have a reference...

But then if it is a floating earth, then the chances of a shock are less unless you go L>N

You need to find out as much as you can about the generator and how it's earthed so you can be prepared ;)

[MrSpeedy]

I expect the generator to be diesel and produce around 10kW

The track has around 2Kw of static draw from floodlamps and a portaloo water heater.

 

It will be grounded, by having the ground output from the generator plugged directly in to the earth (soil/grass)

 

Could you explain more about a floating earth and the issues with earthing?

 

Thank you

Toby

[Junior8]

You're approaching it from the wrong end - you tell the client and they tell their suppliers what YOU require. What you require is a properly protected fused and earthed supply terminating in the kind of outlets you want where you want them. There are plenty of genny hire firms well qualified for this sort of work, it is up to the client to find them - as you point out yourself. If they aren't prepared to do that - don't touch it. One other thing. In the marquee try to position yourself as a far as possible from any seams/joins and the poles in a traditional type - this based on bitter personal experience of working in torrential rain!

[MrSpeedy]

Good point there about positioning within the marquee,

 

I have asked the client and requested a 3 phase 10kW earthed and spike protected, currect regulated this that and the other generator.

 

They have assured me that the generators are, and I quote "The event generators are of a high grade and not like a standard building site type"

 

The overall summary from the organiser was "should be fine..."

 

When im there, I will assess the situation and I will also need to find out what sort of outputs the generator has.

 

I require 13A, would I be right in thinking the generator will not have standard 13A plug outs?

 

Thanks Again

 

Toby

[revbobuk]

Can I add a related question (which may well be obvious to everyone else, but it isn't to me). If I've done what Junior8 describes, and asked for a properly fused, earthed and protected supply with the appropriate outlets - when I turn up, how do I know what quality of earth I have? What's the appropriate bit of test gear to have in my toolkit to check resistance to earth? I imagine that not all of the simple plugin 13A testers will reveal this. What do you carry around with you?

[themadhippy]

Proper tester would be an earth electrode tester,an earth loop impedance tester can also be used ,if an rcd is in the circuit then youll need another tester to check the disconection time and trip current. If its a quick go/no go test then some thing like http://www.pattesters.co.uk/pat-accessorie...ty--rcd-tester/ may work . A very dirty test for operation of rcd's,after checking the polaritys correct is conecting neutral to earth.

[jonathanhill]

I require 13A, would I be right in thinking the generator will not have standard 13A plug outs?

If it does, run for the hills. Generators should only have BS EN 60309-2 connectors and/or a bus chamber. I would take a length of 16A cable, and an inline 16A 30mA RCD (do you know what the generator RCD has been set too? The one behind the panel that comes before all the outlet MCB protection? Is it likely to be set to 30mA? More likely 100mA or higher.) and then convert to 13A inside either via a 16-13 adaptor or a Rubber Box style 16 to 13 distro. By the way 'plug outs' are generally called sockets.

[Junior8]

The installation will be covered by BS7909 anyway won't it? The end user should have nothing to do with the feed between the genny and the structure unless they have a ticket surely?

[Simon Lewis]

I wouldn't really say your going to get any damage asuming you take the basic steps. Whether it's a genset or a little honda petrol toy, it still generates the same flavour of electricity.

 

erm - whilst I'd like to think that's correct, experience has shown that unregulated devices can give significantly higher voltages than expected (the bouncy castle man was not happy when he saw the smoke pouring out of his fan). Also, there can be problems from just using a single phase of a three phase generator, loads with high power factor (if that's not been calculated in) and noise on the supply affecting the audio system.

 

Simon

 

A concurrent post has been automatically merged from this point on.

 

when I turn up, how do I know what quality of earth I have?

 

You ask for the BS7909 completion certificate, which will detail the earthing arrangements, RCD arrangements, deviations from 7909, and that the system has passed visual inspection, polarity, phase rotation, earth fault loop impedance, and RCD operation tests.

 

If you are the "competent person" undertaking these tests, then you will have the usual equipment to carry out test and measurement to 17th edition requirements.

 

If you turn up and the person who has just started up the genny hasn't a clue about the above, then who knows?! Although you can now buy a Martindale tester with a basic earth fault loop impedance indicator (~£50?) it is not a substitute for a proper low Z meter, megger and RCD tester. Expect to pay around £750 for this, and ideally you should fully understand the requirements of both BS7671 and BS7909.

 

Simon

 

Edit to add...

 

Noise from the genny should be considered, as should the requirement for safety of supply for lighting, protection against fuel spill and several other issues mentioned in teh HSE advice on running temporary electrical supplies...

[revbobuk]

Simon - I understand what you are saying, but often that's not where we're starting from. The guy who provided the generator probably left hours ago, and I'm simply doing the sound. I can take it all on trust - but I believe I'm right in saying that systems under 5kW don't need to be certified to BS7909 anyway - or I can do some simple tests. I'm not going to spend £750 plus a couple of courses just to be sure that someone else is doing their job properly, but I would cough up £50 - or even £250 - for a bit of peace of mind.