Maximum Disconnection Times

[Cookie]

What is the reasoning behind having a 0.8 disconnection time for up to 120 volts Uo, but it then jumps to 0.4 seconds as soon as you go over it? Wouldn't it be better 0.8 seconds for 150 volts Uo and under, 0.4 seconds 150 volts and over Uo?

 

[davesparks]

What is the reasoning behind having a 0.8 disconnection time for up to 120 volts Uo, but it then jumps to 0.4 seconds as soon as you go over it? Wouldn't it be better 0.8 seconds for 150 volts Uo and under, 0.4 seconds 150 volts and over Uo?

We don't use 150V supplies, but we do have 110 and 230 so in reality whether you set the limit at 120 or 150 the real world effect will be the same.

What is your logic behind saying its better at 150V rather than 120V?

 

[Cookie]

When using a single phase supply you get 120 volts line to earth, but on a 3 phase supply you get 138 volts to earth which increases the disconnection time requirements (ie faster trip mandated).

 

[Megawatt]

When using a single phase supply you get 120 volts line to earth, but on a 3 phase supply you get 138 volts to earth which increases the disconnection time requirements (ie faster trip mandated).

Cookie I got to be the one but are you asking a question or telling us. Nobody really knows how to respond to the 3 post you have made already.

 

[Cookie]

Asking for the codes reasoning mainly. And if changing it will violate the IEC's body graph.

 

[Megawatt]

Asking for the codes reasoning mainly. And if changing it will violate the IEC's body graph.

Ok sorry I can’t help you have a good day

 

[Cookie]

Well, the NEC does frequently talk about 150 volts to ground over or under. Would be nice to harmonize the IEC with the NEC.

 

[davesparks]

When using a single phase supply you get 120 volts line to earth, but on a 3 phase supply you get 138 volts to earth which increases the disconnection time requirements (ie faster trip mandated).

No we don't, standard single phase and three phase supplies in the UK are 230V to earth.

The 120V would only usually be relevant to a reduced low voltage supply on construction sites.
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Well, the NEC does frequently talk about 150 volts to ground over or under. Would be nice to harmonize the IEC with the NEC.

That will be pretty difficult with the big differences between electrical installations in different countries.

 

[Cookie]

No we don't, standard single phase and three phase supplies in the UK are 230V to earth.

The 120V would only usually be relevant to a reduced low voltage supply on construction sites.
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Yup

That will be pretty difficult with the big differences between electrical installations in different countries.

Usually, but in places like the Philippines, Saudi Arabia and parts of Latin America one is often left working with both codes. An NEC system with IEC standards applied to them.

See page 8:

https://meralcomain.s3-ap-southeast-1.amazonaws.com/documents/presentation/2017-09/meralco-power-up-forum_electrical-design-standards.pdf

120/240 and 138/240Y is found in older installations that have been changed from 120 to 230 volt distribution equipment. Makes for some interesting stuff.

 

[static zap]

What is the reasoning behind having a 0.8 disconnection time for up to 120 volts Uo, but it then jumps to 0.4 seconds as soon as you go over it? Wouldn't it be better 0.8 seconds for 150 volts Uo and under, 0.4 seconds 150 volts and over Uo?

Think of it as Time and "energy Received" , cooking a resistor .
..Where the resistance is a human wishing to survive an electric shock...
Simplify things thinking the first 50V is wasted getting through your skin !
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Think of it as Time and "energy Received" , cooking a resistor .

The reality is we are saving equipment from fire risk , limiting total amount of energy received - is how we stay safe !

 

[Cookie]

Yes, but 0.8 and 0.4 seconds is a big leap. 0.65 might be nice sweet spot.

 

[Cookie]

Why the disagrement on post #3?

 

[DPG]

Why the disagrement on post #3?

Incorrect voltages stated.

 

[Cookie]

How or why are they incorrect...?

 

[DPG]

How or why are they incorrect...?

Single phase to earth. Although are you talking US voltages? Your posts seem to have been asking about UK systems.