Discuss 92 volt touch potential in the Electrical Forum area at ElectriciansForums.net

Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:   American Electrical Advice Forum

Cookie

-
Reaction score
117
I'm really confused by this engineering article. How can the maximum touch voltage be 92 volts on a 230 volt system when in theory it ought to be 115 volts or higher?


In case of a system voltage of 230 Vac phase to neutral, the reason why a time of 0,4 seconds is specified is because 0,4 seconds is the maximum time a person can be subject to 92 Vac. That is the normative touching voltage in a TN system operating at 230 / 400 Vac.

Huh?
 
Very strange, it appears to be a fuse's current/time curve but a "TN" system is so generic that you can't equate a given current (thus clearing time) to a specific touch potential.
 
I'm really confused by this engineering article. How can the maximum touch voltage be 92 volts on a 230 volt system when in theory it ought to be 115 volts or higher?




Huh?
Cookie it’s the neutral not the 120vac. If you lift the neutral while the corresponding breaker is on that’s where you will get bit by 92vac
 
Thinking about it, perhaps the curve they show is the shock risk based on a nominal 2k or whatever skin impedance. I.e. that the limit is 92V for 0.4s

However, that is a rather odd way to present it, as normally the shock risk is better represented by the current (as in the RCD trip characteristics and shock risk).
 
Touch voltage on a TN system is sometimes defined as 0.8 Uo/2 if Rphase = Rpe, giving 92V for 230V systems. But I can't remember for toffee apples where the 0.8 comes from!

it’s the neutral not the 120vac
This is specifically on 400/230V wye systems as used in Europe.
 
Cookie it’s the neutral not the 120vac. If you lift the neutral while the corresponding breaker is on that’s where you will get bit by 92vac


Right, but if you touch hot to ground on a 120 volt circuit, 60 volts will appear at the fault point relative to remote earth before the breaker opens.

Similarly 115 volts would appear to remote earth during a fault.

I can't see where 92 volts comes from.
 
Touch voltage on a TN system is sometimes defined as 0.8 Uo/2 if Rphase = Rpe, giving 92V for 230V systems. But I can't remember for toffee apples where the 0.8 comes from!


This is specifically on 400/230V wye systems as used in Europe.

What is Uo again?

I'd be curious as well on 0.8.

I have a theory that simply shorting out a circuit drops the initial voltage at the spades of a transformer.
 
Right, but if you touch hot to ground on a 120 volt circuit, 60 volts will appear at the fault point relative to remote earth before the breaker opens.

Similarly 115 volts would appear to remote earth during a fault.

I can't see where 92 volts comes from.
I’ll tell you what take a 120vac live wire to ground and see what happens. I don’t see how you can measure voltage by doing that. PS wear protective face shield and glasses
 
I’ll tell you what take a 120vac live wire to ground and see what happens. I don’t see how you can measure voltage by doing that. PS wear protective face shield and glasses


Oscillioscope or if the breaker clearing time is long enough a meter set to its max peak volts setting.

One lead to the EGC at the fault point another lead to an isolated ground rod.

1000 ohm resistor in series if you want to make it more realistic.
 
I can't see where 92 volts comes from.
I think it is very misleading.

I think what they are saying is 92V is the highest acceptable touch potential at 0.4s exposure time. From that you would look at your OCPD current for 0.4s disconnection to set the Ze+R2 upper limit (but they don't say that).
 
I think it is very misleading.

I think what they are saying is 92V is the highest acceptable touch potential at 0.4s exposure time. From that you would look at your OCPD current for 0.4s disconnection to set the Ze+R2 upper limit (but they don't say that).


So how is 0.4 seconds allowed on a 230 volt circuit? 115 volts would be present during a fault.
 
Thinking about this- is it possible they are taking Ze into account with bonding inside the building to water pipes, rebar, ect?
 
Alright- I have a possible answer. I spoke with a seasoned EE. He thinks it has to do with the fact the voltage at the spades of the transformer will drop below 230 volts during the fault. A 32 amp circuit less likely to pull it down considering the run and wire size involved.
 

Reply to 92 volt touch potential in the Electrical Forum area at ElectriciansForums.net

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Electrical Goods - Electrical Tools - Brand Names Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc

Electrical Forum

Welcome to the Electrical Forum at ElectriciansForums.net. The friendliest electrical forum online. General electrical questions and answers can be found in the electrical forum.
This website was designed, optimised and is hosted by Untold Media. Operating under the name Untold Media since 2001.
Back
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock