Backup Generator Questions...

[ukrobj]

We seem to be experiencing a lot of powercuts lately, mainly due to thefts from substations. After returning home with the monthly shop of frozen food and yet another powercut enough was enough. We purchased a generator, http://tinyurl.com/337upwz (Medusa Site Generator T2401).

So its set up to run the fridge freezer in an emergency, however I wanted to ask a couple of questions that you guys might be able to assist with.

I understand that i can only use it up to 2.0kW, so I've been using the watts = amps x volts formula, but reading the manual its expresses it needs to be suitably earthed, so my questions begin...

1) Can the earth be used via the earth terminal block or would i need a earth rod in the ground to solve this?

2) The manual mentions a generator transfer switch, is this where I can Isolate the incoming supply (even if its dead) and then allow the generator to run the supply's to the house, so I could have the boiler and fride freezer running? If so, would you have a rough idea of costs for this?

3) It mentions a power line conditioner for computers and solid state equipment, can you recommend any suppliers for these?

Thanks in advance!
Rob

 

[flameport]

Before you get too involved, you are going down a road which will be expensive and time consuming to provide minimal benefit.

A transfer switch is what would be fitted to your incoming supply to select mains power or the generator. Expect to pay a couple of hundred to have one fitted.

However - a 2kw generator will be useless connected to the whole house - it will just end up being overloaded. It is also possible to damage certain electronic equipment with it (i.e most of the stuff in your house, boiler included).

The generator must be earthed, and also connected to the main earth for the property. An RCD will be required (may have one in the generator already).

Line conditioners are not really what you want - the output from the generator should be via a sinewave inverter if you want to use it for electronic items. These are far more expensive than the generator you have purchased.

 

[ericmark]

The generator must be earthed, and also connected to the main earth for the property. An RCD will be required (may have one in the generator already).

I agree the generator if used for more than one item must be earthed but question connecting to main earth as if PME supply and the supply has failed then you can't use the earth provided by the electricity supplier as it may not be connected to anything.

It will have to be an earth rod and of course a RCD.

I say more than one item because with a single item one is unlikely to get an earth problem in the same way as supply from a shaver socket although really an earth should still be provided.

With 110/220 volt generators one has to be very careful with earths as some I know I had a Honda wired this way don't have earth bonded to neutral but have a 55 - 0 - 165 volt split and care is required.

With food left in an unopened freezer being OK for around 8 hours then to need a generator we must be looking at long power cuts and at 90db I see a problem. At 80db ear defenders are required and so it will need placing in a sound absorbing room. See Control of Noise at Work Regulations 2005.

 

[electronicsuk]

Best just use it as-is with a couple of appliances, extension lead and floating earth for the reasons that have already been mentioned. If you really do have extended power cuts and need to run computers, televisions and the like, you'd be better with a decent Honda inverter generator - expect to pay £700 upwards.

In case you don't believe that cheap generators can damage sensitive electronics, a colleague from work recently asked me to repair the Zig charger unit from his caravan. He'd been feeding it from a small generator similar to the one you've purchased, and some nasties in the electrical supply had taken out a MOV on the input side of the supply. I think he was lucky it did its job and went short circuit, as it probably saved the rest of the unit.

 

[ukrobj]

Thanks for the reply's gents, very helpful. Last couple of power cuts have been about 8-10 hours. Lots of short couple of hours ones, but usually at work for these.

In all honesty, I'm happy with the fridge freezer and a couple of lights, would this cause any issues with the fridge motor?

In respect of the earth, you mention a earth rod and a RCD, can you elaborate on the best way to do this, excuse the ignorance. I'm assuming you wire some 10mm from the generator to the rod (but put a rcd inline?)

thanks
Rob

 

[Spark123]

As ericmark also touched on, small generators do not provide a normal referenced supply. Some require a link to be placed in them (and rodded down) to provide a TN-S supply. Without a Terra supply an RCD is useless.
Using earth rods as a means of earthing is a bit of a foreign subject to a lot of people - they need to be installed and tested using a 3 or 4 wire earth rod tester.
The sizing of the earth depends on the max fault current, installation method and likelyhood of mechanical damage to the cable.
If you want to go with the above I suggest you get a competent electrician to install it.

 

[timtheenchanter]

unlikly to cause a problem with a fridge motor, just make sure it will actually run the freezer, I tried to run a freezer (1/2 expecting it not to work) the freezer rated at 400W, however th startup current is more than the 850Watt genny could give.


I would also consider using filament lamps rather than CFLs, they tolerate the fluctuations better.

You might want to look at making a box for it, 90Db at 4M WILL annoy the neighbours.
last thing, check the run time, it has a max of 13Hrs (or11 depending on the model) this will be no load, the run time will go down significantly under loading.

 

[plugwash]

You only really need an earth rod tester if you are installing rods on a completely remote system. If you have mains available during testing then you can just measure the loop impedance from the mains to the rod. This will overestimate the impedance a bit but that is unlikely to be a problem.

 

[Spark123]

Not according to GN3
You may be pushed to get a reading sub 21ohms using a loop tester.

 

[ericmark]

While you have mains power you can use that as a reference to test an earth rod. The stand alone meter

uses three wires (or four) and you take three readings moving the centre electrode to ensure the area used for testing is big enough and where you don't have a large expanse of ground to place the electrodes in it is often impossible to use. The £300 plus price tag is also a draw back.

However where one has a mains supply one can use the much cheaper earth loop impedance tester to get similar results using the DNO's transformer earth as a reference and these

are both more common and cheaper the one shown is just £145 and most electricians will have one of these.

However it still needs skill and if not used correctly can produce danger. And so really it is not a DIY job. Assuming a TN-C-S supply the rod changes name when supply is there it's an extraneous-conductive-part and when the supply is lost it's an earth electrode as a result 10mm cable is likely required to cover all uses. Under fault conditions there will be a gradient of voltage and so contact to the ground around the earth rod needs limiting so these

are used so one can't get too close.

As to using multi-items from the generator one needs to ensure the two supplies can't be used at the same time. A common method is plug and two sockets and all items to be used with generator have their own mini consumer unit and this is either plugged into the generator or into a socket connected vie a MCB to the main consumer unit. This means some re-wiring and would require notification under Part P. With £100+ charges from local authority this also means not really a DIY job.

So in real terms either an extension lead to run one item or you are looking at a few hundred pounds to set up correctly and being honest what is insurance for? Coupled with the very noisy generator you have selected which will need housing in a sound deading container and have the exhaust and air cooling altered to be able to run in a housing I would have said it's not an option your freezer will have to work without power from 11pm to 7am anyway because of generator noise and you also have an 8 hour plus time where I would assume your at work so the whole thing will only work from 6pm to 11pm any way seems to me a non starter?

 

[JohnD]

However where one has a mains supply one can use the much cheaper earth loop impedance tester to get similar results using the DNO's transformer earth as a reference

excuse my ignorance, but how do you do that? Is it measuring the impedance to the earth rod from a socket on the mains supply? Using the probe like you would to test a water pipe or metal cased appliance?

 

[ericmark]

From meter you take lead to rod rather than DNO's earth. As already said it will read a little on high side but anything under 200 ohms is a pass when using an RCD anyway so good enough.

However you are going to raise the voltage on the rod during the test so measures to ensure no one can touch anything during the tests must be taken.

As I have said not really a DIY job and the installation certificate will need presenting to the LABC so can't be fudged in any way. Got a feeling the 90db will present a problem and think whole idea is really a non starter. If I was presented with the same problem I would use a battery charger and inverter with change over relay. No noise. And will work automatic no need for anyone to swap plugs or start generators. Plus cheaper. Still in theory would need an earth rod of course. But for single item I would not worry.

 

[ukrobj]

Cheers, I know its not ideal, but we all learn from trying different things and I've already learn a fair amount from your comments. In regards to the noise, luckily we have a garage the generator will sit in, the cooling is fine, however I've adapted the exhaust to external air. So although there is a hum its not really noticeable to neighbors. We have it on an extension lead to the fridge, however I do like the idea of a battery and inverter.

 

[ricicle]

If it purely for the freezer then as mentioned above they are normally good for around 8 hours un-opened. If you really want to do it I would just use the generator as stand alone and only plug the freezer in. No need for a rod or RCD. Just use it as a seperated system.

 

[ericmark]

Cheers, I know its not ideal, but we all learn from trying different things and I've already learn a fair amount from your comments. In regards to the noise, luckily we have a garage the generator will sit in, the cooling is fine, however I've adapted the exhaust to external air. So although there is a hum its not really noticeable to neighbors. We have it on an extension lead to the fridge, however I do like the idea of a battery and inverter.

Learn from my mistake I bought an inverter from china at I think it was £129 rated a 3KVA with a 6KVA surge modified sine wave. Seemed great then failed they honoured guarantee but I had to pay transport at £89 by time customs were added so it did not work out cheap and now more problems with it. At a 2.2Kw load starts to smell. So we can only load to 1.5Kw too low to work washing machine.

So if you get an inverter buy from UK don't use Ebay learn from my mistake.

As to fridge/freezer only they would not start on a 180W inverter but run OK on the modified sine wave 3KVA one. And I would consider around 1KVA would be required. 24VDC or above is really required to reduce current and to tie in with any PV system you may use in future don't be temped to use 12VDC.

And as with the generator it does not end with inverter you also need batteries and a battery charger. The stepped battery charger my son uses cost around £250 and the three batteries at 120Ah each another £250 but he lives on a narrow boat so no real option.

For stand-by a cheap CB power supply should charge batteries and keep them on float charge and at about 80W for freezer a 90AH leisure battery should run it continuous for 10 hours so likely it would easy run for 24 hours with freezer switching on and off. If you did use 12VDC then of course you could use jump leads to car but many of the better solar panels need 24VDC so you have to consider both.

Sine wave inverters are better in so far as what they will run but use more power for same output. Although all sorts of warnings about what will not work on a modified sine wave nothing in the boat failed.