Rcd for generator use

[Onthespotwelding]

Hi everyone,

A friend had a recent electric shock, from a dodgy extension lead and standing water.

it's got me worried about my own set up.

Basically I've got a large petrol generator with Extension leads run from it for welder and other tools. All tools are 230v.

Thinking about rcd's like this

RS PRO Inline Mains RCD Connector Inline RCD Adapter 2 Pole ,Rated At 16A,220 → 240 V ac | RS

uk.rs-online.com

Any help and advice is appreciated

 

[Barking Mat]

Your generator if it doesn't have an RCD at power take off, assuming you run a cable off it, should run to a distribution box, containing a RCD, and MCB 's for plugs.

Give me a minute, I'll draw a picture.

 

[GRW]

Hand tools should all be double insulated for one.
Is the genny dual voltage 110/230vac? If yes, then it'll probably be a "floating voltage" (in that the potential between L & N will be say 230vac... but N & E aren't linked - so it is possible to have a small voltage (& current) between N & E on dual voltage sets.
This can cause nuisance tripping of RCD's (though rarely an issue IME).
For gennys bought for house backup, I used to specify 230v single voltage only, with N & E linked - guaranteed no voltage or current between N & E, & no RCD issues.
In any case the RCD will protect cables and loads downstream of it, not anything upstream.... so if a fault caused the frame to become Live - it'll not save you. EVERY generator SHOULD (but portables very rarely are) always have an Earth Rod sunk and connected to the Frame (along with an Earth cable loop from the engine/alternator to frame, so the Anti-vibration mounts aren't insulating the engine from the frame, rendering the Earth Rod ineffective).
Any safely IP67 enclosed RCD in circuit will do, but note most portable sets (even large industrial ones) tend to have adjustable units, as nuisance tripping is a factor (& a royal PITA when you badly need the thing working. Up to 100mA for 0.5s is actually pretty safe for anyone healthy anyway, and 30mA can be just too "fussy" on a genny also.

 

[Onthespotwelding]

Thanks for the replies for a little more clarity here is the genny control panel from the manual.

each socket has a "breaker" but no other info. No mention of rcd's ect

 

[jimbo84]

The best protection with generators is the gear hanging off it. RCDs shouldn't be relied on. Condition of cables, environment, IP ratings and the use of class 2 equipment should be carefully observed.

Earthing arrangements are important and an earth rod isn't always necessary and can make things worse in some cases depending on the generator.

MythBusters #6

This month, James Eade looks at his specialist subject of temporary power and, in particular, the earthing of temporary generator sets.

electrical.theiet.org

 

[jimbo84]

Thanks for the replies for a little more clarity here is the genny control panel from the manual.

each socket has a "breaker" but no other info. No mention of rcd's ect

View attachment 499992

It looks most likely to be a generator that most people would class as a floating earth (not a true term). You should only use one piece of class 1 kit as a fault in that would pose no problem, so long as there was no connection to the mass of earth (hence my earth rod mention in the post above).

For using various class one items each would need its own individual RCD for the RCD(s) to offer any protection. One on its own on the output for various items would do nothing. You're better sticking to class 2 only kit with that type of generator.

 

[GRW]

The best protection with generators is the gear hanging off it. RCDs shouldn't be relied on. Condition of cables, environment, IP ratings and the use of class 2 equipment should be carefully observed.

Earthing arrangements are important and an earth rod isn't always necessary and can make things worse in some cases depending on the generator.

MythBusters #6

This month, James Eade looks at his specialist subject of temporary power and, in particular, the earthing of temporary generator sets.

electrical.theiet.org

You'll need to take the "no earth required" argument up with the authorities then, because an independent earth (at or below 20 ohms resistance really) is demanded.

Backup gennys on buildings usually mains supported - MUST have independent Earth. This is to ensure that whatever incident removed the utility supply didn't also interrupt the Earthing the utility supply relied upon - ensuring the system had an Earth via the genny in use.

I agree that 99% of the time, an RCD will react & protect and mean the earth rod isn't needed as such - but again, it won't Earth the chassis or any metalwork of the generator itself were a fault or short to occur... in such a case the Earth might well be the thing that stops you getting dead.

 

[brightspark]

here you go

https://www.reddit.com/r/WTF/comments/2o6269/a_bucket_of_earth

 

[Onthespotwelding]

here you go

https://www.reddit.com/r/WTF/comments/2o6269/a_bucket_of_earth

Cheap and cheerful What could go wrong!

 

[GRW]

I know of a Council Main HQ that had £50k+ of equipment damage that occurred when their backup genny was disconnected yo be load bank tested (3-years after the building was commissioned).

The installing Electrical Contractor had failed to do 2 things.... 1. Remove the solid neutral link on the changeover switch, and 2, install the neutral link on the Mains. We can only assume that their testing not only failed to puck up on these physically, but didnt notice their test measurements were reliant upon the generator Neutral-Earth link, via the aforementioned solid N link on the changeover panel.

So, wen the genny connections were dropped off (with the entire building on mains.... oops, no Neutral, and lots of stuff gave out magic smoke.

(Contractors tried to throw the genny co under the bus - when they didall the installation & testing, & signed the job off )

 

[jimbo84]

You'll need to take the "no earth required" argument up with the authorities then, because an independent earth (at or below 20 ohms resistance really) is demanded.

Backup gennys on buildings usually mains supported - MUST have independent Earth. This is to ensure that whatever incident removed the utility supply didn't also interrupt the Earthing the utility supply relied upon - ensuring the system had an Earth via the genny in use.

I agree that 99% of the time, an RCD will react & protect and mean the earth rod isn't needed as such - but again, it won't Earth the chassis or any metalwork of the generator itself were a fault or short to occur... in such a case the Earth might well be the thing that stops you getting dead.

That is the case with the generators/installations you're talking about.

Here we're talking about a smaller generator of unknown output and set up. Introducing a rod connected to the earth may not be correct for this generator, as in the IET article I linked it's not just a blanket requirement.

 

[GRW]

That is the case with the generators/installations you're talking about.

Here we're talking about a smaller generator of unknown output and set up. Introducing a rod connected to the earth may not be correct for this generator, as in the IET article I linked it's not just a blanket requirement.

Tbh I read that and I don't think it's entirely accurate, incomplete and totally ignores the "live chassis" scenario.

CTE generators can and are connected to Earth Rods all the time - the fact that the N isn't linked to Earth does not cause them to "fail spectacularly" at all!

I certainly would not rely upon that article, or its author.

As for lagging pf - gennys actually function BETTER on a lagging pf, & use LESS fuel! (The alternator experiences the full current, but the engine does not).

The biggest issue is the amount of non-linear loads now, which cause a build up of voltage & current in the N (Note that a half-size N conductor used to be permitted in installations - now it has to be on par with the Live conductors.... as even the Utility had issues with N burning out.

 

[Robotstar5]

The guy who owns the stables has a genny for his storage building, at least he made an effort with the earth

 

[Jack_K]

An RCD won't function without a EN link and it is unlikely that the generator has one. In most cases an EN link can be added but some generators can't due to being centre tapped.

I don't know the UK requirements and unfortunately I don't even have my local standards documents. In order to follow the standards, we have to pay an overseas company for a copy of the standards. It's around a couple of hundred dollars each and there's probably close to ten different electrical ones.

What I do have is a document specifying how mine site generators should be wired. They suggest against connecting portable generators to the mass of earth but require an EN link and RCD.

"For plug & socket connected generators, the connection of a generating set bonding system to the general mass of earth through an earth electrode is not required or recommended (AS/NZS 3010:2005 Clause 4.2.3)."

https://www.resources.nsw.gov.au/sites/default/files/documents/out10-2110-ees-014-technical-principles-for-the-use-of-stand-alone-generators-_version-2__5_.pdf

 

[Onthespotwelding]

So I've just had a look in the manual and it does say it needs to be grounded when in use. So that's done.

What is mentioned in the manual "below" i also have no clue about, not that i work on metal decking anyway.

ALWAYS use a ground fault circuit interrupter (GFCI) (not included) in highly conductive areas such as metal decking or steel work. Extension cords with an inline GFCI are recommended for these operations.

 

[MetalMonkey]

GFCI = RCD