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Syllabus Sections:-

9d Protective multiple earthing

9f.1 Recall that in PME systems the main earth terminal is connected to the neutral of the electricity service at the consumers' premises and that all metal pipes and fittings within the premises are also connected to the PME bonding point.

Recall that under severe fault conditions PME systems have the potential to cause fatal electric shocks and/or fires in amateur radio stations.

What ever is written here is with regard to the examination.

Altering anything associated with Electrical safety such as tampering with your electrical supply to your residence etc MUST only be carried out by a qualified electrician.

PME

In brief, this method of electricity supply involves bonding all of the house metalwork together, and this will include any radio earth you have provided.

The cross-bonding, at first glance, will negate all the RF good housekeeping; it will bypass the filters carefully installed in the supply leads. To avoid that, the cross-bonding wire should pass through several ferrite rings to provide RF isolation. Some 20 to 30 passes or turns are recommended, which, due to the thickness of the earth wire, will require several rings. 

Potential to fault

Under severe fault conditions, such as when the neutral from the power station fails, a PME systems has the potential to cause fatal electric shocks and/or fires in amateur radio stations. How is this you may ask ? Well all the neutral that would normally go back to the power station will now go to earth through your earth bonding. But not only yours but every ones in the street, (as your earth stake is now acting as the neutral) until you power fuse can take no more and blows. The possibility of electric shock is obvious as all the chassis of your equipment could be raised to mains supply potential, if only for a short time, and if your cables are small over heating of the cables can occur and a fire develop.

Recall that the RF earth in an amateur station should be connected to the PME bonding point in accordance with IEE Wiring Regulations to maintain safety under fault conditions.

The R.F. earth

The R.F. earth in an amateur station was never intended to take mains current to earth and as such should be connected to the PME bonding point in accordance with IEE Wiring Regulations to maintain as much safety as possible under fault conditions.

For your own piece of mind do some more research on this topic by taking advice from your local qualified electrician and by reading the topic mentioned below.

The RSGB EMC committee publishes leaflet EMC 07. you should also read the information enclosed therein. Click here to the links page - we have no control over this page please advise us if the link breaks.




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