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Engineer54
It's called a 3 wire single phase supply, in essence it's a split phase and neutral supply.... 220/240volts between the split phases and 115/120 volts between phase and neutral/earth...
It's called a 3 wire single phase supply, in essence it's a split phase and neutral supply.... 220/240volts between the split phases and 115/120 volts between phase and neutral/earth...
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electric will
2 phases and and a neutral then. Always concerned me over there how they ran larger loads on 115. Sounds a good system probably safer than ours
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Engineer54
Errr, ....you need to think about that statement a little longer me thinks!! lol!!
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nickblake
All the ones ive installed ive installed on a TNCS supply if thats on the house and they are fibre glass and the only metalic parts are within the TUB none have integrated RCD's, main switch RCD and 40 amp MCB if you get a neutral fault then this will cause an imbalance and trip the RCD , in the area i am if you can get an earth rod in more than 300mm you'll be lucky , non of the manufacturers instruction have stated that they require an RCD and i understand about exporting the earth , bit like roding a wooden garden shed supply
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electric will
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Engineer54
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Engineer54
Dont just think of the tub construction material when talking about Class 11, you have pumps and heaters, then think what will pass through them, ..yes water, ...but not just your standard tap water, the water will be treated with chemicals to correct Ph values and others for disinfection to keep it crystal clear, such as Bromine, Algaecide, flocculates, etc etc... Which i would think, will make the water far more conductive than your standard water will be....
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SPARTYKUS
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OldeSparky
Its not just about a fault on the tub, you should TT a hot tub, its all about the potential difference between true earth and the MET (PME)
Its the failure of the PME thats the worry here,
Plus class 1 fittings in and around the tub could be a problem.
personally i would TT a hot tub
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nickblake
yes i do understand so why are we using PME at all because if you loose the supply neutral in a house that has a shower above the a cast iron bath then you have an even worse scenario every piece of bonded metal will become at a potential of around 110 volts so realisticall every PME installation shold be TT just in case
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SPARTYKUS
So you prefer to rely on a device thats proven to be unreliable and subject to high failure rates (the RCD) for disconnection! Theres a lot more chance (probably several orders higher) of the RCD failing than the PME neutral being lost.
Don't get me wrong I am not a fan of PME (TNS all the way) but .... the logic puzzles me. Loss of neutral is unheard of. And fixed quickly the miniscule few times it happens. RCD failure is rife and often never checked, fixed or found. Especially when they're fitted by a "friend" that has 'acquired' the board and RCD and has no registration, invoice, and more importantly, test equipment. Changed a few things for a mate who had the board changed 8 years ago, as above, RCD was kaputt. Probably never worked. How would we know? It was never tested.
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Chr!s
How would you know if the Earth was lost on a TN-S? That's one advantage of PME, the DNO are alerted to it.
Each system come's with risk, non are infallible.
Broken PEN'S, it hapens, quite rare
RCD'S failing, it happens, more down to not testing the RCD quarterly or the system to which it connects to than the RCD itself.
TN-S loss of Earth, it happens, though very little TN-S in most area's now, certainly Domestic anyhow.
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SPARTYKUS
Hi Chr!s
good point re loss of earth on TNS. Not sure. Assume most losses would be because cable is severed or damaged, isn't the outer usually the earth on TNS?
I'm just a cynic and suspect they dropped the idea of having 3 hard lines back to the sub station as it is (clearly) cheaper to have 2 instead.... all about money.
I agree, nothing is infallible.
Not sure about the quarterly testing. I have come across a few that operate satisfactorily on the test button, but do not operate when tested (ramp, x1, etc) and have been replaced). So as mentioned, nothing is infallible including the test button!
TNS a dying breed.
Don't know much about the construction, etc between a house and substation of a TNS cable. Would love to though!
good point re loss of earth on TNS. Not sure. Assume most losses would be because cable is severed or damaged, isn't the outer usually the earth on TNS?
I'm just a cynic and suspect they dropped the idea of having 3 hard lines back to the sub station as it is (clearly) cheaper to have 2 instead.... all about money.
I agree, nothing is infallible.
Not sure about the quarterly testing. I have come across a few that operate satisfactorily on the test button, but do not operate when tested (ramp, x1, etc) and have been replaced). So as mentioned, nothing is infallible including the test button!
TNS a dying breed.
Don't know much about the construction, etc between a house and substation of a TNS cable. Would love to though!
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Knobhead
Don't know much about the construction, etc between a house and substation of a TNS cable. Would love to though!
Here you go!
View attachment 14514
1/ Outer sheath (PVC)
2/ Armouring
3/ Bedding
4/ Sheath (lead or lead alloy)
5/ Fabric tape
6/ Worming (filler)
8/ Insulation
10/ Conductor
The picture is of a MV cable so I've missed some bits out that aren't used for LV
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electric will
That's interesting, so it's not the armour used for the earth conductor, it's a lead sheath which is actually deeper inside the cable
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SPARTYKUS
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electric will
It looks to me that the picture is of a 3 core cable, with a lead sheath then a swa outer for mechanical protection
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SPARTYKUS
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