Andy Wade coughed up some electrons that declared:
No I hadn't - default reaction because I've made off SWA before and it's what I've seen the most of in it's general class.
But... Just had a look, split concentric does look better, 3mm smaller on the diameter and a quid/m less. Is the method of making off just to strip the neutrals and twist into a single form, ditto CPC minus the stripping? Or is there a special method? Google drawing a blank...
Cheers
Tim
Perhaps of academic (rather than practical) note unless your cable route & installation method is to plaster in split concentric :-)
Split Concentric does not comply with 526-06-06 in 17th. No RCD required if the cable is run on the surface, in steel trunking/ conduit, or at >50mm depth etc (note BReg AD "A" imposes limits on wall chasing depth). However RCD would be required if you just buried the cable under plaster. RCD protection of a sub-main is no good because you would lose any final circuit downstream RCD discrimination.
SWA does comply with 526-06-06 in 17th. No RCD required if the cable is just buried under plaster, however the size & min bend radius (6*Dia) probably prevents this anyway.
A comment re EFLI testing. Buy a copy of GN3 re testing. The 15ma no-trip EFLI measurement sounds good, but I am not totally convinced by their efficacy. No trip EFLI measurement is indirect via a complex algorithm & tiny test current. If any noise is present during the test the results can suffer poor reproduceability & accuracy, sensitivity analysis of some algorithms is poor. Noise can occur from fluorescent lights (turn off neighbouring CPD), appliances accidentally left plugged in, proximity to the Tx, harmonics etc, even battery level. Eg, Low current EFLI test may produce Zs results varying from 0.9ohm to 1.4ohm which makes validating a circuit design meets Zs limits for a 40A+ Type-B CPD rather ambiguous. Eg, Low current EFLI test results lose accuracy as Zs gets very low (TN-C-S) - an issue if validating say sub-main fuse protection. Meter accuracy can be a flat +/- 10% or a tighter %age with +/- 4-digit variation to consider. I notice calibration certificates are at high Zs levels, such as 0.7-1.0ohms (TN-S supply Ze).
With a low test current the algorithm is highly sensitive, noise may not be rejected but actually magnified. With high current EFLI tests this does not occur, noise that affects a 15ma test is insignificant in a 25A test - but the high current test will trip an RCD.
EFLI testers are live testers. That exposes you to live testing risks (25A test at light fittings will spark at probes). That exposes you to instrument selection (three wire testers can not be N+E joined to test no-neutral light switches without tripping the RCD). Fused test leads are ideally required, which adds to the cost.
EFLI can be determined dead. Regulations permit calculation of Zs - measure R1+R2 via 200ma continuity meter, obtain Ze from supply-type & DNO enquiry (TN-S
0.80ohm, TN-C-S 0.35ohm) or simply measure Ze. PFC obtained from DNO enquiry. Make up your own wander lead or socket adapter (make buy one with 4mm bridge lead as necessary). Some find hook test leads are quick.Some EFLI meters will measure R1+R2 for you (recent Megger 2-wire testers, LTW325 IIRC) which can save time. Multiple boxes incur multiple calibration charges, single boxes incur less but are a single point of failure.
Just a few comments.
-- DB.
Hi, thanks for the detailed reply :)
snipped-for-privacy@dorothybradbury.co.uk coughed up some electrons that declared:
Thanks for clarifying that. I hadn't got that far, but I guessed that having a neutral (which should be regarded as "live" as much as line/phase) wrapped around the line conductor would not be considered "protection". I have three routes, underground, clipped direct to external wall, via loft space on cable tray.
I'll look into that.
That's very kind - thanks. I have a science background, but it'll take a couple more read throughs to fully digest. I think I need to download some manuals for a couple of potential purchases testers and look into this in more detail.
Cheers
Tim
I'm likely to be in the same position soon. Is it worth upgrading my on-site guide from 16th to 17th?
Andy Dingley coughed up some electrons that declared:
Unfortunately it's not out yet. Mid August is the estimate I last came across and Amazon are saying pre-order for 1/09/2008.
Cheers
Tim
Tim S coughed up some electrons that declared:
Found a random number on the web and managed to get straight through to the department for moving supplies.
Answers:
700 squid (order of magnitude guesstimate on their part) to move an underground cable and relocate supply head from side to front of house. Confirmed that an EIC would be needed, but we didn't go into the why's and wherefore's of registered/non registered person completing said EIC. Didn't go into moving tails or isolators - I'll assume that'll be around 100 quid.I knew I was onto a good thing having found an actual technical department, so decided not to push good fortune too hard in one sitting. So I got the Ze and PFC data out of them, PFC 16kA, Ze 0.35 Ohms. Good, that's one bit of research done.
Went on to asking about earthing arrangements. Given another number and name of person in what turned out to be the uber-technical department.
Really helpful chap there, carefully looked up the records and confirmed that I had TN-S. Result...
Also found a firm of Consulting Electrical Engineers not very far from here. Asked if they'd be up for doing a small job: producing a written calculation on the cable and protection required on a 100A submain, in the context of the service and final circuit protection. They said they didn't mind the odd small job, about 2 hours at 58+VAT/hour. They told me all the information they'd need, which I knew anyway.
Cable sizing isn't particularly hard, but I do want to be confident that there will be adequate discrimination between the submain fuse and all the downstream RCBOs as well as ensuring that the protection at each level is able to operated in the prescribed times.
Reckon I could have a go at the calcs (done the fault disconnect time check already) and I will try the whole thing as an academic excercise, but it's a bit like "having a go" with SuperBeam for the RSJ that's holding my house up. Probably get fairy close with a following wind, but I'm not betting my life on it. Besides, having a formal document will be good for the file and might impress the BCO, we'll see.
Time for further reflection to see if there's any way I can get the CU near the meter without undue compromise. It's a weird house, nothing is obvious, takes a time to come to a conclusion about anything.
We'll see...
Cheers
Tim
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