Live Aerial Mast

Tale Submitted by: Dave Thomas

Again, I wrote this a few years ago but it is just as relevant now as it ever was: LIVE AERIAL MAST.

Here’s some serious advice for anyone climbing up to an aerial.
Never grasp the aerial initially.
Brush the back of your hand against it.
Never hold on to the neighbour’s aerial or aerial fixings whilst
touching your own aerial.
Remember that many aerials have the dipole insulated from the boom, so there’s a shock hazard there as well.

I learnt this the hard way a couple of years ago:

I was called to a new customer who had lost satellite reception. The dish, unusually, was a very good quality one fitted to a solid mast on T+K brackets holding it just above the flat roof of a single storey (fortunately) extension.
I positioned one half of my short extension ladder, climbed up 6 or 7 rungs and grabbed hold of the mast. (other hand still on the ladder, of course).
The mast was at full mains potential.
I have had many shocks in the past but never one like this. They always say that you can’t let go, and its true. My muscles locked and I heard the 50HZ buzz inside my head. I screamed, forced my hand off and fell from the ladder. I can quite safely say I have never been so scared. The customer came running and picked me up. I staggered inside and ordered him not to touch anything.

After a cup of tea etc and a few sessions of seriously frightened shaking, I thought I should, at least, isolate the problem.

Everything in the living room was unplugged from the mains without touching anything metal….the neon screwdriver still showed live on all the aerial leads.
We checked the dish. There was a mains cable to the shed hanging above it, but 12″ away……we followed the cables around the outside of the house, nothing near.
I gingerly unplugged the mast-head amp power supply in the loft….everything still live. I used well insulated pliers to pull out all of the aerial plugs and HDMI’s etc from all of the kit by the TV…..only one cable live now. It was the return from the Sky box to the distribution amp feeding 4 other rooms. The amp was a low voltage one powered from the Sky box. The aerial leads were live at each of the 4 rooms. We carefully unplugged each of the 4 TV’s from the mains, along with VCR’s, DVD’s Play stations and the rest. Unplugging the last TV, in the master bedroom, finally solved the puzzle…..The TV was an ancient Hitachi 14″ portable. It did not have scart sockets or anything other than the aerial socket and it was simply receiving the Sky box distributed around the house as an analogue signal. With the TV isolated from everything else, I plugged it into the mains and tested the aerial socket with the neon screwdriver and it was live. Now I know this is quite common and is usually only leakage so I tested it with the multimeter and it was fully live in relation to the household earth.
At this point, the customer said it should be ok as he had recently had it repaired at a local shop. Apparently the aerial socket on the set had been broken and they had replaced it!
Sets of this age often had live chassis, or at least half mains potential and as they had no other external connections to worry about, the actual aerial socket was isolated with internal capacitors.
The shop had, in their wisdom, replaced it with a standard, non-isolated socket thus passing mains to everything connected to it. How this had not tripped the system….who knows.

Be warned…..!