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ProMbrooke

Disconnection time 120 volts Uo vs 150 volts Uo

Question

ProMbrooke

Is there any real danger in using a 0.8 seconds as disconnection time for 150 volts line to ground? Or would a sweet spot at 0.7 seconds work? Call me cheap but I don't want to use 0.4 seconds unless I really have to.
 

 

 

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Andy™

well table 41.1 requires 0.4 for TN or 0.2 for TT (both AC), so if you want to deviate then you would have to justify that and mark it int he deviations box on your EIC/MWC

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Tony S

@ProMbrooke is American, test certificates don't exist.

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Andy™
7 minutes ago, Tony S said:

@ProMbrooke is American, test certificates don't exist.

 

neither does any form of testing

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kerching
1 hour ago, Andy™ said:

 

neither does any form of testing

Switch on

listen

nothing?

jog on

bang?

get someone in

jog on

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ProMbrooke

But is there really any danger Andy? I don't see a huge increase in danger between 120 and 150 volts line to ground.

3 hours ago, kerching said:

Switch on

listen

nothing?

jog on

bang?

get someone in

jog on

 

 

Lets stick to electrical theory here please :)

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kerching
49 minutes ago, ProMbrooke said:

But is there really any danger Andy? I don't see a huge increase in danger between 120 and 150 volts line to ground.

 

 

Lets stick to electrical theory here please :)

Oh I think you would be unpleasantly surprised at the number of people who subscribe to the aforementioned testing procedure 

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ProMbrooke

Perhaps. But I more interested in the theory.

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binky

OK, in the UK on building sites we use a lot of 110V tools, which gives an RMS value of 50V ish. 50v is regarded as a 'safe' touch voltage, under fault conditions. Clearly the higher the voltage the more risk people are at, but how much difference say an extra 10V adds I don't know. 

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ProMbrooke

True, but remember that in place like the Republic of the Philippines, Saudi Arabia and South America power is distributed line to line. So its 127 to 138 volts line to ground.

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binky

then you need to work with regs pertenent to the country concerned. I'm only familiar with UK regs. 

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ProMbrooke

UK regs are based off of IEC-60364. Same disconnection time is in the IEC. My question is- does a 0.8 second disconnect time really pose any hazard at 150 volts to ground? If so would a 0.65 second timing be ok? 0.4 seems like extra material.

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binky

I'm trying to remeber what the disconnection times were before it all went 0.4?  We suppossedly work on 230V which is roughly 115V to ground and certainly hurts! 

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ProMbrooke

I'd be curious to know. 138 volts is 69 volts to remote earth so I'm not that concerned going over 0.4 seconds.

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binky

it doesn't sound like armeggedon to me :D

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Andy™
On 25/11/2019 at 10:45, binky said:

OK, in the UK on building sites we use a lot of 110V tools, which gives an RMS value of 50V ish. 50v is regarded as a 'safe' touch voltage, under fault conditions. Clearly the higher the voltage the more risk people are at, but how much difference say an extra 10V adds I don't know. 

 

but 110v site supplies are 55v to earth single phase, 63.5v 3 phase. not his 150v to earth

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ProMbrooke

Neither to me.

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binky
43 minutes ago, Andy™ said:

 

but 110v site supplies are 55v to earth single phase, 63.5v 3 phase. not his 150v to earth

is it 150V or 75V ? 150V will kill.

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Andy™
11 minutes ago, binky said:

is it 150V or 75V ? 150V will kill.

 

150v is the voltag the OP is on about. not sure where it comes from

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binky
6 minutes ago, Andy™ said:

 

150v is the voltag the OP is on about. not sure where it comes from

likewise, sounds like foreign places to me

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Tony S

120V or 230V to earth is the norm throughout the world. I'm not sure about Outer Mongolia.

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ProMbrooke
11 hours ago, binky said:

likewise, sounds like foreign places to me

 

 

I'm talking about Uo. On a 138/240 volt Y system Uo is 138 volts. 150 volts at the high end of the 240 volt nominal (260 volts max) supply tolerance.

Edited by ProMbrooke

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ProMbrooke
8 hours ago, Tony S said:

120V or 230V to earth is the norm throughout the world. I'm not sure about Outer Mongolia.

 

 

Not necessarily. Philippines, Saudi Arabia, and parts of South America derive 230 volts line to line.

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Sidewinder

Firstly with faults. It is the U0 Voltage that we are concerned with.

How are you determining the disconnection time, is this a theoretical exercise, a design or calculation, or is it a measured value which when compare to the breaker impedance is giving these disconnection times?

At the instant of the fault the supply live conductor and the protective conductor act as a voltage divider.

To simplify things, lets allow them to be of equal value for a moment, this means at the instant of fault you are dropping half U0 in the line & half U0 in the protective conductor.

The exact values will vary depending on the exact impedances, but for this model 50:50 will do.

So, with U0=120V this gives 60V at the point of the fault, with U0=150V you have 75V.

From this you can look back at the tables and data in IEC 61140 & IEC 61479 and derive the allowable disconnection times.

These times are related to the physiology of the body, expected heart rate, body impedance etc. For the population based on statistical models.

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ProMbrooke
On 28/11/2019 at 03:03, Sidewinder said:

Firstly with faults. It is the U0 Voltage that we are concerned with.

How are you determining the disconnection time, is this a theoretical exercise, a design or calculation, or is it a measured value which when compare to the breaker impedance is giving these disconnection times?

At the instant of the fault the supply live conductor and the protective conductor act as a voltage divider.

To simplify things, lets allow them to be of equal value for a moment, this means at the instant of fault you are dropping half U0 in the line & half U0 in the protective conductor.

The exact values will vary depending on the exact impedances, but for this model 50:50 will do.

So, with U0=120V this gives 60V at the point of the fault, with U0=150V you have 75V.

From this you can look back at the tables and data in IEC 61140 & IEC 61479 and derive the allowable disconnection times.

These times are related to the physiology of the body, expected heart rate, body impedance etc. For the population based on statistical models.

 

 

Well put, my exact thinking. :) But what specifically am I looking for in IEC-61140 and IEC-61479?

 

 

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ProMbrooke
On 26/11/2019 at 19:22, Tony S said:

120V or 230V to earth is the norm throughout the world. I'm not sure about Outer Mongolia.

 

 

I measured the voltage today, got 122.4 volts line one to earth, 122.5 volts line two to earth, and 244.5 - 244.7 volts line to line. 

 

 

 

https://imgur.com/a/UhawBsS

 

 

 

https://imgur.com/a/evv95Pn

 

 

https://imgur.com/a/JyyTdsJ

 

 

https://imgur.com/a/9sx1lWQ

 

 

What would you say?

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