Discuss Maximum Disconnection Times 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

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?
 
Electrical2Go - Online Electrical Supplier
This official sponsor may provide discounts for members

davesparks

-
Mentor
Arms
Esteemed
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?
 
  • Thread Starter Thread Starter
  • #3
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).
 

Attachments

Last edited:

Megawatt

-
Arms
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.
 
  • Thread Starter Thread Starter
  • #5
Asking for the codes reasoning mainly. And if changing it will violate the IEC's body graph.
 

Megawatt

-
Arms
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
 
  • Thread Starter Thread Starter
  • #7
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

-
Mentor
Arms
Esteemed
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.
Post automatically merged:

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.
 
  • Thread Starter Thread Starter
  • #9
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.
Post automatically merged:

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:



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.
 
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 !
Post automatically merged:

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 !
 
Last edited:
  • Thread Starter Thread Starter
  • #12
Why the disagrement on post #3?
 

DPG

-
Arms
Esteemed
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.
 
  • Thread Starter Thread Starter
  • #16
Center tapped 240 is 120. Line to line 240 produces 138.

Republic of the Philippines uses this system.

Yes, BS7671 and IEC codes on how they would go about dealing with those two voltages.

I'm well aware line-line 240 is rare in Europe.
 

DPG

-
Arms
Esteemed
Center tapped 240 is 120. Line to line 240 produces 138.

Republic of the Philippines uses this system.

Yes, BS7671 and IEC codes on how they would go about dealing with those two voltages.

I'm well aware line-line 240 is rare in Europe.
Err OK then.
 
  • Thread Starter Thread Starter
  • #18
Its ok. :) Just this forum is to quick to assume things.
 
Last edited by a moderator:

Megawatt

-
Arms
Center tapped 240 is 120. Line to line 240 produces 138.

Republic of the Philippines uses this system.

Yes, BS7671 and IEC codes on how they would go about dealing with those two voltages.

I'm well aware line-line 240 is rare in Europe.
In a star connection phase to phase is 240 vac phase to earth 120vac the voltage you read can be as high as 130vac the same goes with 3 phase. It’s a plus or minus 5% on the voltage in the US
 

Megawatt

-
Arms
138-139 volts, at 252 volts (+5%) it is 145 volts.
That highest voltage I’ve seen is 130 to ground and where are you getting 138vac
Post automatically merged:

That highest voltage I’ve seen is 130 to ground and where are you getting 138vac
Your drawings are irrelevant that’s not telling us nothing
 
  • Thread Starter Thread Starter
  • #22
130 volts would be the highest in a 120/208 system, not a 240 volt wye system.

The drawings are correct for the system being depicted.
 
Also got a post deleted in another thread for saying the stuff on Amazon made by China is often not safe to install.
Tricky tight rope - Negative opinions ..
( I'm older and just love moaning )
You get what you pay for, (and some local wholesalers risk a big hit , when they have to honour their returns policy)
Need to educate customers to spend more!
 
  • Thread Starter Thread Starter
  • #24
Education is key. Which is why I spoke up. But shady manufacturers/sellers know people buy solely based on cost.
 

Megawatt

-
Arms
130 volts would be the highest in a 120/208 system, not a 240 volt wye system.

The drawings are correct for the system being depicted.
On paper is one thing, in the real world it’s a totally different world. Why the emphasis on exactly 138vac
 

Megawatt

-
Arms
Where's my post gone? I was sticking up for the forum!!!
I’m from the US and we don’t have those kind arrangements
 
  • Thread Starter Thread Starter
  • #30
Asking about the code's reasoning. And Megawatt- I fully get you!
 
uHeat Banner - Forum Discount Available
This official sponsor may provide discounts for members

Reply to Maximum Disconnection Times in the Electrical Forum area at ElectriciansForums.net

Aico 3000 Range
This official sponsor may provide discounts for members
Top Bottom