er... whats PME got to do with this?
and what exactly is your argument, since it seems to be changing every other post...? (would be nice to know exactly what your trying to say, since its not very clear)
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and what exactly is your argument, since it seems to be changing every other post...? (would be nice to know exactly what your trying to say, since its not very clear)
[quote name='Andy
so what happens now that we have NO rod from star point?
nothing...
but.... what exactly does PME have to do with thread? the genny is rodded to earth, and the installation is fed by a TNS supply from the genny....
anyway, now that you have made your little drawing, please state exactly how the TNS supply form the genny is automatically made into TT....
[quote name='Andy
steps,
direct contact no matter what the supply configuration is will give the IP a shock via what you describe as a TT system.
I'm NOT getting into semantics.
The DNO supply is earthed via a rod, as they all are at the local HV/LV transformer, we'll ignore the bit inbetween the direct contact between the IP and the live conductor whilst direct contact will result in a TT system for the fault current.
The consumers electrode will be the IP.
I fail to see from the laws of physics how this can be different for any conficuration of supply and consumers installation.
Direct contact, NO EEB, NO ADS based on Zs will assist.
The only thing that is going to protect you is additional protection or shock current limiting due to the nature of the TT resistance created by the high resistances between the origin electrode and the IP.
The current will still be enough to kill and the voltage will be high enough to force that voltage through the IP.
I fail to see how a correctly designed TT system can protect you in this situation any more than can a TN-S or TN-C-S.
If you can elaborate on your position (I hate to call it an argument) as it is as has been suggested open dabate, how you propose that a TT system will limit the fault current and voltage to below letha levels in such a scenario / all scenarios then I would like to know.
Please provide calculations, regulations and legislation to back up your position so we can analyse this against "the laws of physics Captain"
I'm NOT saying your wrong or right, I just need to understand the science and engineering upon which your position is based, as from the sketch you have provided, which is not wrong and is now clear, I cannot see the point you wish to make.
How about providing some sample calcs on how your proposal reduces the fault current and voltage to non lethal levels as defined in standards and legislation. I can't remember the document number for the shock resistance levels which are quoted in BS's etc.
This may help to assess the shock potential of any installed system and to analyse how the fixed wiring affects the potential tissue and CNS damage to the IP.
direct contact no matter what the supply configuration is will give the IP a shock via what you describe as a TT system.
I'm NOT getting into semantics.
The DNO supply is earthed via a rod, as they all are at the local HV/LV transformer, we'll ignore the bit inbetween the direct contact between the IP and the live conductor whilst direct contact will result in a TT system for the fault current.
The consumers electrode will be the IP.
I fail to see from the laws of physics how this can be different for any conficuration of supply and consumers installation.
Direct contact, NO EEB, NO ADS based on Zs will assist.
The only thing that is going to protect you is additional protection or shock current limiting due to the nature of the TT resistance created by the high resistances between the origin electrode and the IP.
The current will still be enough to kill and the voltage will be high enough to force that voltage through the IP.
I fail to see how a correctly designed TT system can protect you in this situation any more than can a TN-S or TN-C-S.
If you can elaborate on your position (I hate to call it an argument) as it is as has been suggested open dabate, how you propose that a TT system will limit the fault current and voltage to below letha levels in such a scenario / all scenarios then I would like to know.
Please provide calculations, regulations and legislation to back up your position so we can analyse this against "the laws of physics Captain"
I'm NOT saying your wrong or right, I just need to understand the science and engineering upon which your position is based, as from the sketch you have provided, which is not wrong and is now clear, I cannot see the point you wish to make.
How about providing some sample calcs on how your proposal reduces the fault current and voltage to non lethal levels as defined in standards and legislation. I can't remember the document number for the shock resistance levels which are quoted in BS's etc.
This may help to assess the shock potential of any installed system and to analyse how the fixed wiring affects the potential tissue and CNS damage to the IP.
[quote name='Andy
my very point is SIDEWINDER that under a fault condition your install will undertake a (virtual{if you will})TT install, so why not design it as TT from the outset and not rely on TN to start with.steps,direct contact no matter what the supply configuration is will give the IP a shock via what you describe as a TT system.
I'm NOT getting into semantics.
The DNO supply is earthed via a rod, as they all are at the local HV/LV transformer, we'll ignore the bit inbetween the direct contact between the IP and the live conductor whilst direct contact will result in a TT system for the fault current.
The consumers electrode will be the IP.
I fail to see from the laws of physics how this can be different for any conficuration of supply and consumers installation.
Direct contact, NO EEB, NO ADS based on Zs will assist.
The only thing that is going to protect you is additional protection or shock current limiting due to the nature of the TT resistance created by the high resistances between the origin electrode and the IP.
The current will still be enough to kill and the voltage will be high enough to force that voltage through the IP.
I fail to see how a correctly designed TT system can protect you in this situation any more than can a TN-S or TN-C-S.
If you can elaborate on your position (I hate to call it an argument) as it is as has been suggested open dabate, how you propose that a TT system will limit the fault current and voltage to below letha levels in such a scenario / all scenarios then I would like to know.
Please provide calculations, regulations and legislation to back up your position so we can analyse this against "the laws of physics Captain"
I'm NOT saying your wrong or right, I just need to understand the science and engineering upon which your position is based, as from the sketch you have provided, which is not wrong and is now clear, I cannot see the point you wish to make.
How about providing some sample calcs on how your proposal reduces the fault current and voltage to non lethal levels as defined in standards and legislation. I can't remember the document number for the shock resistance levels which are quoted in BS's etc.
This may help to assess the shock potential of any installed system and to analyse how the fixed wiring affects the potential tissue and CNS damage to the IP.
all the calcs you require will be found in BRB as most people seem so fond of quoting.
in pic 2, he wont get a shock. no return path. same as theory as SELV
your example of how TNCS earth voltage can vary from ground is valid... but only for TNCS.
it does not apply to TT or TNS! at no point in the installation is there a TNC part, so ground voltage will always be at earth voltage because of the rod....
now if you took TNC from the genny to installation, with a rod at star, and then split to TNCS at installation, then i agree there could be a slight difference between earth and ground
Any TN system in the national grid is rodded at the star point for compliance with statutory regs, so I'm not sure of your point steps?
philbas
Well-known member
OK I
you have not shown in any way how the installation has became TT...
unless you magically install a rod to installation, and ditch supply earth at the exact time of someone getting a shock, the installation will always remain TNS (or TNCS)
neither am i... apparantly a TNS system changes to TT when you get a shock....
green-hornet
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[quote name='Andy
but why TT it... you have full controlI think the point being made is why change from TT to TN? why not just leave it all TT?I like TT it confirms earth
why make it TT?
if you make it TT, then a fault live - metallic case will have limited fault current, and (hopefully) trip the RCD. if it doesnt, then there may be a voltage between installation earth and ground
keep it TNS, then the same fault will have a nice low resistance back to star, and a larger fault current to take out any MCB/fuse aswell as RCD, with very little voltage between earth & ground during the fault...
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