Postby blacknight » Sat Apr 26, 2008 3:57 pm

HI,i have a 2 pin socket in the garden of the new house weve just moved into.It was professional fitted as i found the reciept.This was for a hot tub.
I want to change it to a normal 3 pin socket,for outside lights,mowers etc.All i can tell you is its a 32amp 250v.Is there an easy soloution to this.Thanks. :?
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Joined: Sat Apr 26, 2008 3:53 pm


Simply Build It

Postby ericmark » Sat Apr 26, 2008 7:46 pm

If the socket was "professional fitted" there should be an installation certificate to go with it with more details.
Two pin would normally be only used for extra low voltage and the only socket I can think of with two pins for 230 volt is a Rayrolle type where the aluminum casing carries the earth. These were popular before the standard blue plastic type came in and often the pins were fuses.
The problem is the earth and where a socket supplies a special piece of equipment it may not be good enough for general use and before converting and earth loop impedance test should be done to ensure it is OK but this should have been done when originally fitted and should only be a case of checking paperwork. If you can't find it the firm who fitted in in first place should have a copy think they need to hold for 10 years.

Postby blacknight » Sun Apr 27, 2008 8:33 am

Hi,found the paperwork & certificate,is was fitted july 2007.Installed a SWA AND 20a socket and test.On the p/work under circuit impedences is says r1 + r2 is 0.11 and r2 n/a.Does this help,because i dont really understand it.Thanks.
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Joined: Sat Apr 26, 2008 3:53 pm

Postby ericmark » Sun Apr 27, 2008 12:00 pm

The cable is OK for your outdoor type of 13 amp socket fitted at that date it should be RCD protected. As to if you can do it yourself under Part P it is gray area. You are allowed to swap like for like in a special location but swapping one type of socket for another may not be seen as like for like and may require building controls notifying under Part P. There are links and you can look yourself. If you are DIY then careful on socket selection it is hard to connect a SWA cable to non metallic sockets. Norm is to mount socket inside a box or enclosure to give protection from rain etc. Often will lockable door to stop kids playing with it.

Postby ericmark » Sun Apr 27, 2008 5:07 pm

Just to explain your paperwork. R1 + R2 is the resistance measured at one end of the cable when the line is connected to earth at the other end and is used to work out if there was a fault would enough current flow to ensure the protection device will operate within the prescribed time.
In the electricians bible BS7671 it gives tables so we can check these results. Since we consider 50 volts to be the maximum a normal person can survive it is all worked out at 50 volts rather than 230 volts to ensure even if something goes wrong and the supply volts dropped to 50 volts it would still work.
When the supply authority give you your supply they measure earth loop impedance and tell you what it is or with a TT supply the electrician who installs the earth rod measures it.
From the tables we can see a 20 amp type B circuit breaker needs a resistance lower than 2.3 ohms to trip in 0.4 seconds.
If we add the typical 0.1 earth loop impedance at the consumer unit to the 0.11 ohms of R1 + R2 then 0.21 is well below the 2.3 required from the table.
For a garden supply we should also have an RCD these require a lot less current to flow in order to trip and is more like 1667 ohms but because that value would likely be unstable we say 200 ohms is required.
In your case I wanted to know with a two pin plug was there any earth at all. And the fact that you have reading confirms to me there is an earth.
R2 is just the earth wire ohms and if we have R1 + R2 we don’t need it so N/A stands for not applicable.
I was in a bit of a hurry at first post. As electricians we have a problem in giving advice in that it is so easy for people to have problems with what we think is easy and missing out bits which we assume they would know anyway. Small SWA to me is easy but I know other have problems especially when trying to gland into plastic boxes a simple 6mm brass bolt into the banjo washer to get an earth is all well and good when you have brass bolts in your box, ring terminals and crimping pliers I hope it goes well for you.

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