Presumed RF Interference

Matthew Sullivan matthew at
Mon Mar 6 10:17:17 UTC 2006


Peter Dambier wrote:

> Cut the ground wire in your power cords but ground the equipment directly
> to a metal frame.

As a time-served electrician... *****DO NOT DO THIS***** - it will kill 


You could try separate earth bonding of each components (ie connecting 
all the chassis together via a provided grounding terminal using nice 
thick copper wire), however if there is a significant earth fault even 
that could be dangerous (think fire) - so get a qualified electrician to 
do it - if there is a ground fault it will use the chassis and the 
bonded earths as it's route to ground.

Earth faults are often easily detectable by using a digital volt meter 
(Note: analog volt meters do not work for this unless there is a serious 
fault).  First check for induced and ungrounded 'floating' voltages (any 
AC or DC voltage above 0.05v should be investigated), then if the DVM is 
fused, check for any current (amps) between chassis.

If you have money to spend before investigation find out if the building 
has a grounding stake and if not add one...  A couple of meters of 
copper stake which  will be connected to either the armoring of the 
supply cable (TN-S) or to the incoming return cable and installation 
earth PME (TN-C-S) - likely based what someone else in this threat 
said.  In either type of grounding scheme the structure metal frame 
could (and should) be grounded (esp if exposed) which is likely to cause 
the phone RF signal drop.  A faulty bonding in the structure (esp as it 
is steal) can also provide for some interesting ground faults as it is 
not uncommon to provide localised grounding to building frames.  (In the 
UK where I served my apprenticeship, we were required to provide earth 
bonding to the copper plumbing system, additional bonding at every 
exposed fitting - this caused a few issues when plumbers first starting 
using PVC pipes)... All this said with the faults appearing with no 
external power and with just UPS supply, ground faults really do not 
'fit' the problem - however if a generator is used also, you are in an 
IT type installation (electrical term 'IT' not 'Information Technology' 
;-)) and will have to have a grounding stake on site.

Please note, I am trained from the UK - laws and regulations change from 
country to country - get a local qualified/licensed sparky to do the 
work or assist you.



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