K
keefy
Just finishing off cert for a TT system, got a Zs of 115 ohms throughout. will I be right in thinking the max Zs column for all circuits will be 1667 or 200?
Cheers
Cheers
G
Guest123
That would depend on what rating of RCD you have protecting the circuits....
The 200ohm value is the max recommended by BS 7671 for the installation Ra.
K
keefy
A 100ma type s at the cut out as it is a short distance from the DB and a dual 30ma RCD in the board as it is a domestic property.
Cheers
Cheers
M
MarkieSparkie
The 30mA RCD additionally protected final circuits will have a Zs maximum of 1667 Ohms.
For a non time delayed 100mA your maximum Zs would be 500 ohms, if all the circuits are protected by the 30mA RCDs then max Zs is 1667 ohms.
Ra x I delta n <= 50V
so 50V/0.03s = 1667 ohms
50V/ 0.1s = 500 ohms
The time delay causes problems for disconnection times as it will add about 0.15s to the time.
Ra x I delta n <= 50V
so 50V/0.03s = 1667 ohms
50V/ 0.1s = 500 ohms
The time delay causes problems for disconnection times as it will add about 0.15s to the time.
E
Engineer54
But still well worth having as a supplementary back-up for those 30mA RCD units, on a UK installed TT system with an Ra of 115 ohms wouldn't you say?? lol!!!
Nice low Ra like that! Well yeah I think so, you are pretty much as safe with a 100mA as a 30mA gone in 0.02 seconds, or 0.17s better than .4s whatever. (sorry, of course the regulations, forgot about them: 100mA deadly!)
R
Rauer
One of my mates was testing for the council and on tt systems they wanted him to link the neutral to the earth at the board ( so in theory it's a tn system) to get more "true" zs readings
E
Engineer54
You sure they didn't mean ''False'' reading?? lol!!
R
Rauer
I did think to myself ......hang on a minute!!! But I suppose they would satisfy the maximum zs for a change!!!! Not quite sure how the nic etc. would like it tho, but it was the councils head electrician that told him!
T
trev
What would be the point of linking those conductors? Any reading given would be completely worthless
R
Rauer
Pass!!!!
E
Engineer54
S
Specialist
After telling someone to do that I think i'd be leaning towards the Sacking option myself.
R
Rauer
Completely agree hence why I have never done it!! But the councils don't make sense either! He was first subb'd in as an installer , if he did anything they weren't happy with he had to go back and sort it , then they had him as a test engineer and he had to put installers work right if it wasn't!!!
T
trev
Which asylum oops sorry I meant council was this?
R
Rauer
Warwick!!
S
Specialist
Think you got it right the first time trev, looks like the Lunatics are takeing over the Assylum again:yesnod: :crazy:
Merry Christmas mate:christmastree1::santa3:
G
Geordie Spark
Don't talk to me about council's head electricians !!!
Some years ago, our council declared our area a General Improvement Area & offered private homeowners a grant to improve their properties. Such improvements included new guttering, new garden walls, fences gates etc. & as my house was in need of new gutters, a new front garden wall & a new back gate I applied.
The next thing was we had a visit from their inspector who agreed that we could be elligible for this grant, subject to a satisfactory report from their Electrical Inspector. No problem I thought, as I had only recently completed rewiring the place.
The Inspector arrived a few days later when I was at work & he left my wife with a report in which he condemned the installation on the grounds that it didn't comply with th council's rules & regulations !!! He was kind enough to leave us with a copy of said regulations, which were based on the 15th edition (which I had worked to) but with a lot of other silly stuff added. Wife said that he had hinted that if we "greased his palm" everything would be ok & we would get our grant, other wise "the whole lot will have to be ripped-out & done again".
Wife's parents lived up the road in a council house which had just been renovated & that included a complete rewire, so off I went to inspect their installation & was horrified to find that many of the old fittings - some of which were broken & held together with insulating tape - were still in use. Further investigation revealed cables under the floor running in notched joists which according to the council's own regs. wasn't permitted, and cbles literally wrapped around central heating pipes, when their regs. clearly stated that they should not even be in the same void !!
So, armed with a neatly writen list of my findings, I presented myself in the Head Electrician's office which wasn't much more than a janitor's cupboard literally under the stairs of the Town Hall. I presented him with my findings & told him in no uncertain terms that if I didn't get my grant, I would see to it that he wouldn't have his job for much longer !!!
I got my grant.
R
Rauer
To be honest mate I'm not surprised about the install being shoddy as I did a stint of re-wiring for the council and they were expecting 2 of us to complete a house every three days and only work between 8and 5
ringer
-
I don't understand (the bit highlighted above).
Are you saying that on each and every circuit you measured a max Zs of 115ohms?
Or is 115ohms the Ze of the installation?
E
Engineer54
Don't talk to me about council's head electricians !!!
Some years ago, our council declared our area a General Improvement Area & offered private homeowners a grant to improve their properties. Such improvements included new guttering, new garden walls, fences gates etc. & as my house was in need of new gutters, a new front garden wall & a new back gate I applied.
The next thing was we had a visit from their inspector who agreed that we could be elligible for this grant, subject to a satisfactory report from their Electrical Inspector. No problem I thought, as I had only recently completed rewiring the place.
The Inspector arrived a few days later when I was at work & he left my wife with a report in which he condemned the installation on the grounds that it didn't comply with th council's rules & regulations !!! He was kind enough to leave us with a copy of said regulations, which were based on the 15th edition (which I had worked to) but with a lot of other silly stuff added. Wife said that he had hinted that if we "greased his palm" everything would be ok & we would get our grant, other wise "the whole lot will have to be ripped-out & done again".
Wife's parents lived up the road in a council house which had just been renovated & that included a complete rewire, so off I went to inspect their installation & was horrified to find that many of the old fittings - some of which were broken & held together with insulating tape - were still in use. Further investigation revealed cables under the floor running in notched joists which according to the council's own regs. wasn't permitted, and cbles literally wrapped around central heating pipes, when their regs. clearly stated that they should not even be in the same void !!
So, armed with a neatly writen list of my findings, I presented myself in the Head Electrician's office which wasn't much more than a janitor's cupboard literally under the stairs of the Town Hall. I presented him with my findings & told him in no uncertain terms that if I didn't get my grant, I would see to it that he wouldn't have his job for much longer !!!
I got my grant.
You generally find that those Qualified Engineers of all disciplines, employed by Local Councils are those that couldn't hack it out in the real world. I would imagine that would also go, for so-called ''Head Electricians''!! Probably little Hitlers, that try and make-up there own rules as they go along to suit themselves.
G
Geordie Spark
I think you hit the nail on the head there !!
Most of this bloke's gripes with my job concerned the heights at which I mounted my sockets & switches. They were fine according to one of the chief engineer blokes of the leccy board who was a family friend & was steering me through this - my very first rewire - and the "regs" that were in force at that time, & he did the inspection & testing too.
The council's own "regs" was a 40 something page booklet A4 size that most sparky types I showed it to thought was completely OTT & ridiculous. When I inspected the council's own work, I really struggled to find anything that complied with their own "regs".
I notice that our council no longer seems to have their own "regs" & booklet anymore.
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