lamp post keys.....
- Thread starter ChrisRogers
- Start date
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OK - I'm back on track now.FWL_Engineer said:
I think....
B
Big_Spark
ban-all-sheds said:OK - I'm back on track now.
I think....
Don't worry, I read it a couple of times again afterwards to make sure!! Maybe my warped mind reads it different to others as I wrote it?
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Big_Spark
kendor said:
Kendor..You want to say what is on your mind instead of silly inuendo.
S
Stod
FWL – don’t you think that a 1200 A fuse is a little oversized to protect a feeder to a a few nearby houses and a street light? Isn’t the current rating of a 25 sq mm service cable somewhat less than 1200 A? After all, you size a fuse according to the current carrying capacity of the circuit it protects. So a 2.5 sq mm cable has a maximum fuse capacity of 20 A for example.
Perhaps the 1200 A is the rupturing capacity, although that seems too low. For example, a BS88 fuse typically has a rupturing capacity of 40 kA.
Perhaps the 1200 A is the rupturing capacity, although that seems too low. For example, a BS88 fuse typically has a rupturing capacity of 40 kA.
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Big_Spark
Stod, without wishing to get into a disagreement, to be perfectly honest I only know what I have stated. Beyond that, it is an area of the industry I have not had a great deal of experience of.
I do know the fuses I have seen personally have been 1200A, sometimes smaller and on two occasions bigger.
TBH, I only know what LEB (now 24/7) engineers and other Grid engineers have told me beyond what I have seen.
I do know that there is variation around the country.
In London, many cables that feed street lights, also feed the houses in those roads, normally with one cable up each side of the street. These cables are usually concentric, oil impregnated SWA's in the order of 70mm and larger. The cables that enter homes and street lighting is tee'd off this using cable joints. This is one part I do know as I have been involved in that area many years ago.
If you think about it, normally you get about 20 houses per sub-feeder plus the street lamps (this is only a general set-up), even allowing for diversity, that cable will require at least a 1000A fuse to handle the potential loads, so 1200A is not unreasonable.
I do appreciate that around the country, and even in London, there will be many variations of this sort of set-up.
I do know the fuses I have seen personally have been 1200A, sometimes smaller and on two occasions bigger.
TBH, I only know what LEB (now 24/7) engineers and other Grid engineers have told me beyond what I have seen.
I do know that there is variation around the country.
In London, many cables that feed street lights, also feed the houses in those roads, normally with one cable up each side of the street. These cables are usually concentric, oil impregnated SWA's in the order of 70mm and larger. The cables that enter homes and street lighting is tee'd off this using cable joints. This is one part I do know as I have been involved in that area many years ago.
If you think about it, normally you get about 20 houses per sub-feeder plus the street lamps (this is only a general set-up), even allowing for diversity, that cable will require at least a 1000A fuse to handle the potential loads, so 1200A is not unreasonable.
I do appreciate that around the country, and even in London, there will be many variations of this sort of set-up.
For reference, local street lamps in my area appear to be fed with simple 2.5sqmm T&E, and this fed a 6amp fuse in the lamp.
That is, local kids had smashed the cover off the lamp, and I have not been illegally tampering with streetlights.
That is, local kids had smashed the cover off the lamp, and I have not been illegally tampering with streetlights.
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Big_Spark
sterose said:
What your seeing in the lamp-post is the section of the circuit that has been tee'd off the main cable. Sometimes this is done for each individual lamp-post, sometimes they will take one feed off, and then loop it through about a dozen posts, then do it all over again from another tee'd section.
I managed to find this old schematic drawing in my old college work. I scaned it in, although the quality is a bit rough and ready.
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Big_Spark
The relevence was aimed not at you, but at those who were trying to state that 1200A fuses do not exist in the public grid.
Maybe they also wish to call the LEB(24/7) and the National Grid and tell them they are wrong as they are DIYers and thus know more!!
Maybe they also wish to call the LEB(24/7) and the National Grid and tell them they are wrong as they are DIYers and thus know more!!
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