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Chat => Tech Chat => Topic started by: Weaver on August 11, 2018, 09:44:00 AM

Title: Generator safety
Post by: Weaver on August 11, 2018, 09:44:00 AM
I keep repeatedly telling my dear wife about electrical safety. Our petrol generator is out in the shed. Unfortunately it just puts out its power by being plugged straight into a three pin mains socket. If she were to do so and turn it on she could electrocute any electricity board staff working on the line who think the power is off, or power all the houses in the village. So I tell her again and again that the entire house must first be disconnected from the external supply and I require her to show me that this has been done. However I would like to have more layers of protection against mistakes.

The discipline currently is that I have to be given the 100A main house fuse link first, so my possessing this proves to me that Janet has disconnected the house from the external feed. Then she is allowed to turn the generator on. This only works provided it is not forgotten.

I have an idea or two, but none that are foolproof. The simplest one is to lock the generator up in a box and only I have the key but this is bound to go wrong. I have other ideas too which are not complete and not robust enough.

Can anyone with a brain think of anything really foolproof ?
Title: Re: Generator safety
Post by: d2d4j on August 11, 2018, 10:18:00 AM
Hi weaver

We use Datacentre power auto switches, which have dual power feeds in, and also switch isolation to switch to secondary power feed (say UPS or additional power feed), so the entire power circuit feeding anything attached to the outputs remain normal.

These are very very expensive and mostly not available in the UK

We did not wire these, a fully qualified electrician wired them. Mains power frightens me.

My best advice is to speak with an electrician

Also, if I understand your post, I do not think you are legally allowed to touch that 100A fuse

Many thanks

Title: Re: Generator safety
Post by: Weaver on August 11, 2018, 10:51:25 AM
Regarding the 100A fuse. This is just an OTT safety measure and is not the only way of doing things. The electricity board man who came to wire the house up to the grid explicitly left the seal off the 100A fuse so that we could disconnect things as at the time I was indeed doing the entire house from scratch as it was nearly a ruin. I used to be able in those days. I chopped lots of logs and chainsawed lots of tree trunks 20 years ago. I seem to remember hearing something to the effect that the law in England, at any rate, has changed in subsequent decades and nowadays you are supposed to get an electrician to do some things in your house. I am not sure we have any laws in the Highlands and Islands :-)  :o  (Apart from planning permission, thieving, drugs and speeding laws concerning which certainly do exist.)

We don't need to use the 100A fuse of course. Could just throw the switch at the main box. But I do that so that I have an absolute guarantee that the right thing has been done. If I am holding the fuse the house can not possibly be connected.

One idea that had come to me was to make up a cable from the generator to a wall socket which had an in-line break in it. This break is bridged or not by plugging that same 100A fuse, having been removed from its usual place, into a second fuse holder socket purchased for the purpose and wired in-line.

This is the best plan that I have been able to come up with so far.
Title: Re: Generator safety
Post by: siofjofj on August 11, 2018, 12:14:28 PM
The most foolproof method is to put a changeover switch (eg between your electricity meter and consumer unit (job for an electrician to install really). These are basically double-pole-double-throw switches, with the common terminals connected to the house, one set of switch terminals connected to the incoming mains and the other set to a suitable wall mounted male plug (eg which can be connected to the generator with a suitable cable. With this arrangement, it is impossible to back power the grid from the generator.

I assume you are currently using a lead with a 13A male plug on both ends to connect the house to the generator? These are generally referred to in the trade as 'widow makers', since with one end plugged in the other has live exposed pins. Another advantage of the above arrangement is that your generator lead will have a male plug on one end and a female socket on the other, so nothing live is ever exposed.
Title: Re: Generator safety
Post by: Weaver on August 11, 2018, 12:25:21 PM
As for 'widow makers' I can't remember what the lead is currently. If I had seen such a thing, plug to plug, it would have been gone as quick as you like. :-)

I am grateful for those tips! The difficulty is that the consumer unit is absolutely nowhere near the generator, generator is in a shed because of noise and carbon monoxide. (Has some ventilation so the generator can get more O2 in.)

I am quite a stickler for electrical safety, my wife having had a washing machine burst into flames because the motor jammed while I was out at work when we were in London, my friendís house in West Yorkshire ruined by a similar appliance fire, a fire in the optics laboratory at university when my mains-powered handheld mini red-light torch melted and took out all underfloor wiring, the university's chemistry department burned down after a calculator caught fire, one of my best friends burned a hole right through his finger by shorting the mains out with it, my mother got an electric shock due to 1950s wiring when I was young and my sister burned out a wall socket in her bedroom. So I am always moaning on about RCDs, correct fuse ratings, earthing and so on and pestering my wife to keep a comprehensive range of smaller-rated varied fuses in stock.
Title: Re: Generator safety
Post by: siofjofj on August 11, 2018, 12:56:31 PM
Thanks for the reassurances  :) . To be honest though, if you don't have some changeover arrangement I don't see how you can avoid the possibility of live plug pins appearing somewhere. The generator must have a female socket of some sort on it, otherwise when the generator is running there'd be live pins there. The lead that goes to the house must therefore have a male plug (on the generator end) in order to mate with this. Hence, if the lead is connected to the house while mains is on, you will have live pins on the generator end.

I can't admit to doing this correctly myself though. I have a 'powercon' connector at the house end which has no exposed pins on either the male or female connector, but the generator connection is a 13A plug (since the generator outlet is a 13A socket) so too suffers this issue. In my case however the system is more controlled as I keep the lead locked up somewhere only I have access, so under informed family members can't do anything with it. I realise this is not a practical option for you though.

Going back to the changeover switch arrangement, I guess that a very long extension lead with a 16A plug on one end and a 16A socket on the other is not an acceptable solution (it wouldn't be for me). The trouble is that if you want to do this right, a changeover switch on the incoming supply is really the only option (indeed as I understand it this is the only arrangement permitted by the wiring regulations where the generator is not capable of synchronising to the incoming supply, for which there are pages and pages of requirements to be met). One could perhaps do something with a contactor (big relay) on the incoming supply interlocked with a second where the generator is connected such that both can never be on at once, but this would still require wiring between them.

I assume your current arrangement feeds the house via some pre existing dedicated circuit that supplies the shed. Do you actually use anything in the shed that requires power? If not, one possible solution is to re-purpose the cable going between the consumer unit and shed as the generator supply cable. The end at the consumer unit would be moved to one input of the changeover switch, and the end in the shed would go to a wall mounted male plug.

If that isn't an option, is may be possible to neatly install a new cable between the consumer unit area and shed for this purpose.
Title: Re: Generator safety
Post by: Weaver on August 11, 2018, 01:10:54 PM
That is indeed what I had thought of. Since I can not do any of the work myself any more as I am too ill, I will put it down on the list of jobs for my friend who is a commercial electrician and is coming up to stay with us and wants some jobs because he gets bored just being a tourist.

But as for widow makers, I shall have to check as I simply cannot remember but I will have reviewed it in the first place.

The part you pointed me towards is the kind of thing I was looking for though.
Title: Re: Generator safety
Post by: d2d4j on August 11, 2018, 01:37:24 PM

I hope you donít mind, I am not an electrician but thereís some things which donít add up

Standard houses have 60A fitted so a 100A would indicate you draw/use more then 60A

So I do not understand how your generator can feed a House with a 100A fuse, when it is only rated at 13A over a line which is 16A. So the most it can pull safely is 13A, or if upgrading plug fuse, then it is 16A wire rating

I understand you may say you turn off or do not use high powered devices but itís just something I wondered about

Many thanks

Title: Re: Generator safety
Post by: Weaver on August 11, 2018, 02:05:33 PM
Er, if any high powered devices are left on, which they are not because I am fully aware of the issue and have a whip round, as part of a checklist, then that will simply blow the small fuse I have put inline with the generator and it is as simple as that. In addition the generator has a current-limiter cut-off and will not supply more than about 8A anyway. There simply is not any possibility of supplying 100A down this 13A wallsocket.

It would be a mistake to assume that I am not aware of the issues, but I am indeed very much fallible. :-)

In any case, I have no desire to supply a whole house, it is not intended to be like an office or a hospital.

The only permitted items are UPS for core networking, TV and central heating pump. All other MCBs are thrown as part of the checklist in order to elicited the possibility of certain devices being left on or getting turned on by mistake later. Lighting MCBs are all off, kitchen is off. Only the TV lounge and office MCBS are enabled and kettles heaters in bedrooms are unplugged as part of a checklist for Janet.

The 100A thing is something you should ask the electricity board about. I cannot answer for their choices. I could draw a lot more than 100A by shorting something out using a thick nail but we tend not to. :-)

The purpose of this thread is to help get ideas for safety improvements so all input greatly appreciated. :-)

Will get a chance to get some free help out of my electrician friend anyway when he comes up from North Yorkshire. Amazingly, by sheer coincidence, he is a Theoretical Physics student too, like me, same university even, but a lot younger.
Title: Re: Generator safety
Post by: siofjofj on August 11, 2018, 04:02:46 PM
Standard houses have 60A fitted so a 100A would indicate you draw/use more then 60A

As a general rule of thumb it is only older properties that have a 60A fuse fitted. Newer properties tend to be 100A or 80A, though in the 80A case the enclosure is often marked 100A. I believe most DNOs (distribution network operators) will upgrade the fuse from 60A for free if requested, provided this is actually possible given the loading of the network.
Title: Re: Generator safety
Post by: sevenlayermuddle on August 11, 2018, 06:39:09 PM
I wonder... would it be possible to install a fuse socket, compatible with the 100A fuse, in series with the generator?

Then the generator would only work when the 100A fuse was in place.   Its purpose, when in the generator circuit, would not be to act as fuse, but to act as a kind of mutex, ensuring that the generator could not be connected until after the supply had been disconnected.  This idea would break down if you were to stock up on more 100A fuses, but I see no reason youíd want to do that.

Title: Re: Generator safety
Post by: Weaver on August 11, 2018, 08:55:22 PM
You and I are thinking alike, sevenlayermuddle - mutex indeed, exactly: that was the best idea I was able to come up with!

The widow-maker point comes in again; would not want any exposed metal in the socket because someone could leave the generator-to-mutex-fuse-socket-to-wallsocket cable in the shed live due to juice supplied from one end or the other. So I ought to think of a physical arrangement to sort that issue out.

Was something like that, but mechanical, employed on the railway in the old days?
Title: Re: Generator safety
Post by: burakkucat on August 11, 2018, 10:52:19 PM
I think your electrician friend will be the best person to advise, and install the necessary, when he comes to stay.
Title: Re: Generator safety
Post by: Ronski on August 12, 2018, 08:13:26 AM
You really should not be pulling that main fuse, it can be extremely dangerous, as I understand when power is on live terminals are exposed. You've already said Janet has bad hands, what would happen if she slipped????

Get your electrician friend to fit a change over switch that can also be correctly wired back to the generator.

Have you also considered that each time you remove/replace the fuse you are weakening the connection, eventually it won't make good contact and will get hot. I bet they don't have a high duty cycle.

Title: Re: Generator safety
Post by: Weaver on August 12, 2018, 09:07:00 AM
As I may have said, we don't have to pull the fuse of course, can simply throw the main switch. I initiated this as a measure to prove to me that no dangerous mistake had been made forgetting to disconnect the house or reconnecting too soon.

A job for Steve then. This is exactly why I asked the question, for varied input.
Title: Re: Generator safety
Post by: Starman on August 18, 2018, 09:45:03 PM
turn it on she could electrocute any electricity board staff working on the line who think the power is off, or power all the houses in the village.

Weaver I work for a DNO [The old Eastern board] and I appreciate the concern :)

However I cannot recommend a customer pulling their own cutout fuse to isolate their supply but I understand your reasons.

I think its safe to say unless you have a very large generator the initial load current from picking up the local LV feeder way(s) and possibly inverting into the HV network is likely to cause the generator to at least trip or more likely fail to start at all.

Can anyone with a brain think of anything really foolproof ?

I would suggest you contact your electricity supplier to install a 100A double pole isolation switch located after DNO owned cutout but before your suppliers meter - this will allow you to isolate your installation from the public network.

Some styles do allow you to install a single key safety lock which means without the key you cannot operate the switch or remove it easily (its what we use on the network to secure isolated LV feeder ways or HV switches).

Finally I know some people who have their own generator installation a on-load or offload bypass switch can be installed which would also achieve the same as above.
Title: Re: Generator safety
Post by: jelv on August 18, 2018, 10:51:49 PM
How about a really simple solution? Attach the key to the generator shed to the 100A fuse!
Title: Re: Generator safety
Post by: Starman on August 19, 2018, 06:27:11 AM
How about a really simple solution? Attach the key to the generator shed to the 100A fuse!

I wouldn't suggest a screw ;)

However this stuff would work great!