Cut Outs and Floods

[bernardgreen]

Have any DNO's been relocating their cut outs to be above the high water marks of houses flooded last year ?

Or will they stick the (apparent) policy of flooded areas going off power by manual switch off or auto breakers coming out at substations.

 

[Lectrician]

Has anyone ever recieved a shock or died?

The close proximity of the phase and neutral in a service head will result in a nice short path for any current that does manage to flow. It is not going to 'liven' the water as people believe.

 

[ColJack]

problem with that is, the current is seeking earth, not neutral...

so in TNS systems it's not heading for the adjacent neutral..

 

[efiste2]

"going off power by manual switch off or auto breakers coming out at substations."

Can only speak for SCOT POWER but as far as LV MAINS cables are concerned, the only protection that is between your domestic cut-out and the local 11000/433 transformer is a HRC 315A fuse that can only be manually removed and inserted.........and in urban networks this mains cable can be fed from both ends, But i would imagine a good flood across a number of cut-outs would take these fuses out.

with all the technology and safety devices that are installed in consumer properties these days, its easy to forget that the SUPPLY side of the business is a very much simplified and coarsely protected affair, and in most cases very old........

 

[Lectrician]

problem with that is, the current is seeking earth, not neutral...

so in TNS systems it's not heading for the adjacent neutral..

Nope - Think about it

The current is going to flow to neutral or earth - and the close proximity of the neutral, regardless of earthing type, is going to encourage some flow. The close proximity of the lovelly lead sheath on a TN-S would also help.






There is no set rule as to what fuse is going to be protecting a part of a network. 300amp is typical. There are many modern sub stations with ACB's and MCCB's. Many networks are constructed for redundancy, being able to be fed from one end or the other from different subs, but they are not fed sequencially for sustained periods - only during a switch from one supply to the other.

 

[bernardgreen]

The person who asked me is concerned about the build up of gas ( oxygen and hydrogen in explosive ratios ) from the electrolysis of water around a submerged cutout that is still live.

 

[plugwash]

problem with that is, the current is seeking earth, not neutral...

so in TNS systems it's not heading for the adjacent neutral..

bullsh1t, neutral and earth are (or at least should be) at about the same potential and so for theese purposes can be considered equivilent.

 

[efiste2]

All interconnected HV/LV substations in the SCOT POWER Manweb region only have an ACB to isolate the HV transformer from the LV distribution board, if the HIGH VOLTAGE has a fault or extreme overcurrent. If the substation isnt LV interconnected, it doesnt even have that, But all that protects the LV mains cables is a 315A fuse, i have never seen a MCCB in any network sub........ thats for most U/G networks anyway, in urban areas where an HV protection system called SOLKOR is used the LV main is fed from BOTH ends,

 

[tim west]

dont bother asking others, Steve is the expert on this subject

 

[mst]

what is a ACB?

 

[Lectrician]

All interconnected HV/LV substations in the SCOT POWER Manweb region only have an ACB to isolate the HV transformer from the LV distribution board, if the HIGH VOLTAGE has a fault or extreme overcurrent. If the substation isnt LV interconnected, it doesnt even have that, But all that protects the LV mains cables is a 315A fuse, i have never seen a MCCB in any network sub........ thats for most U/G networks anyway, in urban areas where an HV protection system called SOLKOR is used the LV main is fed from BOTH ends,

I have seen several Merlin Gerin ones recently

 

[Spark123]

what is a ACB?

Air Circuit Breaker

 

[ColJack]

problem with that is, the current is seeking earth, not neutral...

so in TNS systems it's not heading for the adjacent neutral..

bullsh1t, neutral and earth are (or at least should be) at about the same potential and so for theese purposes can be considered equivilent.

not true at all..

the potential of the earth under your feet and the neutral in your hand may be different in a tns system..

the neutral is earthed at the transformer, but if its a significant distance, then the cable resistance could be more than the resistance through you to earth..

electricity seeks earth potential and will take the path of least resistance..

 

[Lectrician]

I do not agree.

A copper or metalic path is going to be a far lower resistance than mother earth.

The lead sheath of a TN-S, or the copper of a TN-C-S (or indeed TN-S) is going to take the current.

 

[ColJack]

in your scenario then, if we disconnected all the neutral / star points of the transformers from earth, then no one would ever get a shock unless they touched live and neutral since the fault current could not run through the general mass of earth to the star point..