We have a horsebox with living accomodation. On board 240V generator to power lights, 13A sockets, battery chargers etc. Is there a way that an RCD, or similar device, can be incorporated to protect any person in case they come into contact with live at any point? Should both the neutral and earth be wired to the chassis of the vehicle.
I once got an electric shock when i put the key in the door of my bus- rubber tyres, me standing on the ground- so now i hammer a spike into the ground and attach an earth wire to it..
I wonder what the experts will say?
[g]
Thanks George,
I need, and other users need, to avoid electric shocks but for other reasons a ground spike is not feasible. VaBene
Make up a steel plate, connect to generator earth, and park one wheel over it.
Just a warning -- horses and other livestock are extremely sensitive to electric shock (more so than humans), and it's important that any design or changes to the wiring are made by someone who is aware of the methods used to prevent electrocution of livestock.
If you connect the generator neutral line to the vehicle chassis, your RCD will act on any shock from the live, it will be fully effective. Your earth connection is then also the vehicle chassis. This is an IT system.
Connection to external ground isn't needed if the electrics are contained wholly within the vehicle. However if leads to the ouside are used then you do need to earth the vehicle chassis.
PS there's a chance that one side of the gen already connects to chassis, and it might be the one you're currently treating as 'live.' If so, grounding the neutral would pop the breaker. If this happens, ground the other gen output line instead, and make sure your fusing etc is in what is now the live line.
All this describes the practicalities of portable generator fault / shock protection rather than being a statement of the full requirements of the 17th edition, which will be more demanding in your case.
PPS you'll want a passive RCD, not an active one. If you get the wrong type you'll have to press the reset button every time you start the gen to get power.
NT
On Tue, 27 Jan 2009 23:02:08 -0000 someone who may be "VaBene" wrote this:-
The 17th Edition covers installations where animals are present and caravans. I imagine that horses are valuable to you. If this is the case then pay someone to give you advice, not a house electrician but someone who understands the issues.
Large four legged animals are particularly vulnerable to voltage gradients.
If you ground the Neutral *before* you take it to an RCD, it should work.
A number of generators output 240V as 120V either side of earth so the line and neutral are each 120V different from their earth.
There has been much useful advice already given but it is worth saying that "some" generators deliver from a centre tapped output winding. Make certain yours is not one of them.
It will certainly be worth you getting hold of a copy of BS7671 and reading up thoroughly on the particular requirements of section 717. Page 206 shows a diagrammatic outline for use with a generating set within or without the unit. Also worth reading up on Agricultural installations in the same BS
If it is, grounding one leg will simply pop the breaker each time it starts. If this happens, whichever leg you ground, then you'll know.
NT
If he has a generator with a centre tap connection to earth and he then earths one output before his protective device the net result is a short circuit of half of the output winding. Running the generator engine will risk burning out that half winding. (Assuming the generator will excite with a short circuit output - some do some don't)
I've come across a gen that has 110-0-110 with the 0 earthed. This possibility needs to be checked for /before/ earthing one side, otherwise cables will melt (as they did in this case).
I assumed the OP would be earthing the gen after its built-in breaker rather than taking the gen apart. If it were shorted pre-breaker, and the excitation system still functioned, the engine would simply stall.
NT
I don't recall any mention of a built-in breaker and certainly my 1.5 kVA geny does not have one. The risk of burning out the winding remains as I seriously doubt mine with its 4 stroke engine and throttle governor would stall under the described conditions. The OP can make his own mind up if he wants to take the risk. Not knowing exactly what model he has I will not make assumptions.
What voltage does the genny winding drop at full load? 10%? Most likely rather less. That means even on a relatively high resistance gen, if shorted it would supply 10x rated curent at normal run speed. If the OP has a generator thats physically capable of doing even a fraction of that speed under such a load, then s/he has a remarkably badly designed gen bought from a company that must have gone out of business very fast indeed. In short, its unrealistic.
NT
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