[TCUG] Re: 6 year electrical testing
- From: Keith Brunt <keithbrunt@xxxxxxxxxxxxxxxxxxxxxxx>
- To: "'tcug@xxxxxxxxxxxxx'" <tcug@xxxxxxxxxxxxx>
- Date: Tue, 15 Jun 2004 15:17:16 +0100
You have to remember the ELI test merely evaluates the circuits performance
to provide fault current large enough to disconnect the fuse protecting the
said circuit.
The test normally looked for is the resistance value of the circuit (Zs) and
to see that it is lower than that of the value for the protecting fuse. The
fuses normally found on phase drive cards are not in the regs and so if you
consider these are the ones protecting the cables out to the signal poles
then you need to work out a value for them. I did submit these a while back.
Never the less the eli test will indicate if the SWA still has sound
connections and therefore eliminates the need for disconnecting any
circuits. This is deemed ok as we avoid disruption to traffic control and
the ensuing dangers. The circuit is then assumed to be safe 'n' sound and
any subsequent faults such as a live wire touching any metalwork will be
safely disconnected by the fuse blowing - this is the principle of
protection form the IEE regs - EEBADs.
One last thing for those who may remember my presentation on electrical
design. Remember the short movie with a fuse exploding? I evaluated the
performance of the phase drive fuse, and found that the glass version, so
often supplied with controller, to be unsuitable for disconnection of large
fault currents in the order of 1000 or 2000amps when used in conjunction
with a 20 or 30amp signal fuse. The answer if to ensure you have the ceramic
version installed not the glass type.
Keith Brunt
-----Original Message-----
From: Bill Emett [mailto:bill.emett@xxxxxxxxxxxxxxxxxxxxxxx]
Sent: 15 June 2004 14:44
To: tcug@xxxxxxxxxxxxx
Subject: [TCUG] Re: 6 year electrical testing
Why would you need to disconnect all cores at pole top, surely only one
core would be necessary to form a circuit to test and an ELI test will
also prove armoring.
Most courses on this subject relate to house wiring which suggests you
only have to test 20% of the system this should reduce the down time if
applied to signals. Unless this 20% shows a problem then the whole
system has to be checked.
One of the queries I have is with E.L.I testing at poles is as
follows,
Our contractors tell me they use a spare live feed but this would only
test straight from the origin via whatever fuse they use to the pole
back via the armored cable and the usual Manweb path to the substation
this is bound to give a favourable result.
This can't give the practical reading via the phase drive circuits
which are essentially in series and have there own resistance which must
be included in the E.L.I figure.
A figure quoted for a max E.L.I test for a particular controller is 5
ohms which is down to the 10A fuse on the phase drive card, not the main
20 or 30 amp fuse in the supply which this figure would fail.
>>> chris.gladwyn@xxxxxxxxxxxxxxxxxx 15-Jun-04 1:33:39 pm >>>
I am currently looking at TCUG guidance Note 1 which in section 2.4.7
suggests that core to core testing may be omitted as there is a
possibility of :-
1. Reduced safety for highway users whilst installation inoperative
for
lengthy periods (perhaps up to 3 days at complex sites).
2. Insecure reconnection of cables especially on older installations.
3. Incorrect retermination of cables at either street equipment or
controller.
4. Additional traffic congestion while temporary arrangements in
operation.
5. Loss of special facilities (pedestrians, cycles, bus priority) for
long periods
Whilst I agree with this the document then recommends that the
continuity of the steel wire armour be tested. The test procedure for
this is to disconnect every core at the pole cap and then connect all
cores together and connect to the SWA.
Surely some of the arguments for core to core testing apply to this as
well.
Does anyone have advice on this and is there an alternative test that
could be carried out that would meet the requirements of BS7671
without
having to disconnect all connections in the pole cap.
Chris Gladwyn
Hertfordshire Highways
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