Although it can be calculated it still must tested to prove compliance with BS5750. Thanks for the info on types of fuses in phase drive cards,I was given the impression by a contractor that they were to BS 88 seems not. >>> Paul.Welsh@xxxxxxxxxxxxxxxxxx 15-Jun-04 3:19:31 pm >>> It is the impedance that matters. It must be low enough to ensure that the fuze blows as specified. With the live feed impedance and drive impedance known, this can be readily calculated. Dave Thompson did a piece on this a couple of years back. Noting the "test every pedestal" comment, rember the pedestal isn't enough every remote point on every pedestal. Once set up at a pedestal, it doesn't take long, open each head, test, record, open the push button, test, record, test the pedestal earth bond and record. The worst part is walking around with the ladder and removing the pole cap. PW -----Original Message----- From: Bill Emett [mailto:bill.emett@xxxxxxxxxxxxxxxxxxxxxxx] Sent: 15 June 2004 15:12 To: tcug@xxxxxxxxxxxxx Subject: [TCUG] Re: 6 year electrical testing I also agree with a test on all poles, also that damage could occure to the lamp drives during testing, but as the lamp drives form part of the path to the pole then they would have to be included in any ELI results to prove a low enough impedance to isolate the pole within 5s of a live short to the pole. >>> Paul.Welsh@xxxxxxxxxxxxxxxxxx 15-Jun-04 2:54:06 pm >>> The acceptable impedance has to take account of the actual circuit. The fuse used for the test needs to have a reasonable value to ensure that it withstands the test current. Which is why testing through the lamp drives should be avoided, it could damage them. There are claims that they should not be damaged, but why take a risk of abusing a device not designed for the test load? As for 20% testing, don't risk it! Remember there have been knock downs etc in the preceding six years, this isn't a nice cosy house, it is a much harsher environment. The site file should have copied of impedance tests from each repair, but are they being done/recorded? (If not why not?) The six year test updates the whole site record and needs to be completed and filed. PW -----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 >>> ************************************************************************ This email contains confidential information, solely for the person/organisation intended. 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