Genny Help

[wreck-it-steve]

Hi,

Ive been given a small portable generator for my remote shed to power some lights and a socket.. im just wanting to know how it all needs to be earthed? Is it treated like a TT system and would it be best to run from the 230v genny socket to a small consumer unit for lighting and sockets?

Any help would be great.

Thanks

 

[bernardgreen]

A TT system has its Neutral connected to Ground at the substation.

A TT system relies on the ground to complete the circuit for any fault currents due to Live to Earth or Neutral to Earth fault in the buildings supplied by the TT system.

So unless the Neutral of the generator is connected to ground there will be no current flowing through Live to Earth or Neutral to Earth faults to trip RCDs.

Likewise there will be no current through a person touching Live and Earth at the same time so the risk of electric shock ( Live to Earth ) is almost eliminated if the generator's Neutral is not earthed.

To my mind having the generator's Neutral intentionally earthed such that RCDs will trip is a safer over all option as it cannot be ensured that the generator output is never accidently connected to ground by dampness, damage, or other un-intentional means.

 

[eveares]

Most portable generators do not have neutral and earth connected together like a typical sub station that supplies houses in a street.

They are often this way due to their nature of being portable and the impracticality of installing earth rods in a lot of locations. They effectively have no useful earth connection, preventing earth faults as their is no return path for earth faults to neutral.

However while their may be no intentional connection between earth and neutral; dampness, damage and other means may cause such a connection between earth and neutral and thus may cause a dangerous situation between a earth fault with an appliance and contact with the generators chassis.

If the generator is a permanent or semi-permanent instillation, then you may want to link neutral and earth together at the generators end and install a earth rod at the generators end in case of earth faults going through the physical ground. This way a RCD will work.

Note doing this will likely invalidate any guarantees and could be dangerous if not done properly.

Elliott

 

[ericmark]

In general any connection of earth to neutral should be inside the generator so unless there is a terminal provided to earth with then you really need to read instructions carefully before earthing anything.

It will be a TN-S or an IT supply depending if the neutral is bonded to earth in the generator. Our tooth brush outlet in a bathroom is an IT supply which is very safe for a single item but not for multi-items.

So a small generator running a drill does not really need an earth. A small generator powering 3 caravans however would.

So with class II lighting and a single socket there is no real reason to worry about an earth rod but with a array of sockets then maybe you should.

Often a socket and a switched fuse connection unit of lights is all that is required there is no need for a consumer unit.

However I consider portable to be less than 28kg which would likely mean an output of 1 kVA or less. But I have worked on generators with wheels up to 68 kVA and container type up to 750 kVA and as a permanent fixture up to 750 MW and we have no idea what you mean by portable.

I steel shed is different to a wood shed and left connected 24/7 is different to carrying it there every day and plugging in.

If I took my father-in-laws generator to my friends woodland for a one off event I would not bother knocking in earth rods. But as a permanent fixture I would.

So a little more info please.

 

[ericmark]

If the generator is a permanent or semi-permanent instillation, then you may want to link neutral and earth together at the generators end and install a earth rod at the generators end in case of earth faults going through the physical ground. This way a RCD will work.

Note doing this will likely invalidate any guarantees and could be dangerous if not done properly.

Elliott

Be very careful before connecting a neutral to earth to ensure there is not already a connection to earth inside the generators. Some generators are designed to be able to provide either 230 volt or 110 volt even though it may not have any 110 volt outlets. When this is done sometimes a tapping 55 volts from neutral is used as an earth so in 110 volt mode it has 55-0-55 volt output.

If this is the case and you link earth and neutral outside the generator you are causing a direct short and could burn out the generator.

So unless you are very certain you know how the generator is wired then best to assume any connection between neutral and earth is done inside the generator don't do it any where else.

 

[JohnW2]

... Our tooth brush outlet in a bathroom is an IT supply which is very safe for a single item but not for multi-items. ...

As a matter of detail, your tooth brush outlet is surely "floating" (i.e. "II"), not really IT - the "T" of IT implies/requires a local connection to earth.

... So a small generator running a drill does not really need an earth. A small generator powering 3 caravans however would. ... So with class II lighting and a single socket there is no real reason to worry about an earth rod but with a array of sockets then maybe you should.

I keep reading things like that, but I don't fully understand. ... AIUI, the only hazard resulting from multiple items on a floating supply arises if there are multiple Class I loads whose exposed-c-ps are not bonded together. As I see it, if they are bonded (via CPCs which are all joined together somewhere), the situation is safe, regardless of whether or not those CPCs are also connected to earth. In other words, the issue is that of bonding the exposed-c-ps together, not earthing. In fact, as has been said, if one could be certain (which one probably rarely can) that an 'accidental/incidental' connection from the genny output to earth was never going to arise, it would probably be safer not to earth the CPCs.

Kind Regards, John