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  • #41
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Err OK then.

I measured the voltage today and got 122.4 volts slot one to earth, 122.5 volts slot two to earth and 244.5-244.7 volts slot to slot. I can't find or measure any 240 volts to earth. IMO the diagrams are correct.
 

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  • #43
These in post #3:




1575139885471.png




IMO they are the correct depiction of the systems I'm working with.
 

DPG

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Advent Win
Sorry, my mistake - I thought you had put 'incorrect'.
Post automatically merged:

I think I need to reread this thread. You posted a table from the UK regs I think, but you are asking about the US voltages? Apologies if I'm confused.
 
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  • #45
My apologies. And to be fair I can understand any confusion this may cause as these systems are not used in the UK.
Post automatically merged:

120/240 and 138/240Y system, not used in the UK, but designing around IEC standards in regards to human and life safety.
 
Last edited:

davesparks

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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.
BS7671 is primarily intended for use in the UK with our standard voltages.

Using BS7671 in the Philippines with USA standard supplies and voltages is never going to be fully compatible. Its a square peg and round hole situation.
 
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  • #47
BS7671 is primarily intended for use in the UK with our standard voltages.

Using BS7671 in the Philippines with USA standard supplies and voltages is never going to be fully compatible. Its a square peg and round hole situation.

I agree- which, IMO- gives me grounds to question Table 41.1 in BS7671 and IEC60364-4-41. IMO both these codes are 230 volts centric, meaning they give little thought when dealing with systems 150 volts to ground and under. Considering that at one point parts of central Europe were 127/220 (think how schuko sockets came about having no polarity), the IEC/VDE/NFC15-100 may have had incentive to mandate 0.4 seconds disconnection times on 127/220 volts systems since an increase in voltage would not require any re-wiring or recalculating of the circuits once raised to 220 volts to ground.

Both the Phillipines, Mexico, Canada and the US use the NEC or NEC based code- however the NEC has no earth fault loop impedance requirements. Meaning I could legally run 2.08mm2 to a shed 2000 feet away and never trip a breaker during a short circuit. All the earth wires in the shed would be at 60 volts to remote earth. I could plug in something metal, have it sit live at 60 volts to ground, get killed, and absolutely nothing could be done to blame the electrician, authority having jurisdiction or the NFPA. Even better a 277 volt light pole in a parking lot. I could run 3,500 feet of 3.31mm2 to a LED light, have a ground fault in the fixture, energize the pole at 138 volts to ground and have it sit continuously 24/7 live without tripping a breaker where a child could hug or lick the post with their tongue during winter. Child dies, case gets taken to court, lawyers litigate away from the real cause taking advantage of everyone lacking basic electrical theory...

Here are two US sparks having seen the problem in their career:




The thing is people, especially children, get killed all the time in the US from energized pools, fences, light poles, AC units, industrial equipment, doors, ect. The blame gets put on shoddy work or poorly connected earth wires... not the code... Much like in the 70s missing bonding jumpers leading to shocks and electrocutions were blamed on ground rods not driven deep enough in the court of law.


The NFPA's solution is to quietly mandate GFCIs on everything- much like GFCIs took care of all the 2 prong metal framed tools injuring people. I encourage you to read the code making panel's reasoning:

NEC 2020 code new standards in GFCI protection - http://www.p3-inc.com/blog/entry/nec-2020-code-new-standards-in-gfci-protection


Ditto for industrial equipment violating earth fault loop impedance:




Which is why I am so curious about learning BS7671 and establishing a value which can be applied to US systems.

That and the fact the US will eventually one day go to a 230-250 volts utilization voltage. Before (if) 230/400Y becomes the norm 127/220, 133/230 and 138/240Y systems will be common in aiding the conversion process. Its easier to raise a Con Edison 120/208Y network by 10 volts than it is by 110 volts.

But regardless the issue of loop impedance (or lack there of) needs to be addressed first.
 
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  • #48
BS7671 is primarily intended for use in the UK with our standard voltages.

Using BS7671 in the Philippines with USA standard supplies and voltages is never going to be fully compatible. Its a square peg and round hole situation.

I'll ask this: how did loop impedance become a thing in the UK? Was it actual shocking electrics or a theoretical perspective of "what if"?
 

static zap

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Advent Win
I'll ask this: how did loop impedance become a thing in the UK?
I wonder if UK DNO. (Supplies) are over engineered !
Uk electrician then feels obliged to maintain the "Earth" integrity for rest of instal - Need an instrument to confirm the status.
 
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  • #50
If you mean the CPC then I think thats a good idea. But testing earth rods on a TN-C-S and TN-S network I think is not necessary.
 
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  • #52
Off topic- but what do you prefer/think is better: TN-C-S or TT?

Personally I wish the world had TN-S without the neutral distributed.
 

static zap

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Advent Win
Good solid copper connections , without reliance on -expensive -Historic lead - Greyness !
(we have fracking -greed to worry about - too !)
(admittedly -my opinions are more from an interested engineer-Than full spec Spark)
 
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  • #56
Well- in TN-S without the noddle distributed you call always have 4 cores around what ever protects the cable :p
 

davesparks

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If you mean the CPC then I think thats a good idea. But testing earth rods on a TN-C-S and TN-S network I think is not necessary.
8f you don't test the earth rods then how do you know that they are providing a low enough impedance to earth?
 

davesparks

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I'll ask this: how did loop impedance become a thing in the UK? Was it actual shocking electrics or a theoretical perspective of "what if"?
Loop impedance has always existed, its a property of any electrical supply, its the knowledge, awareness and testing etc which has developed over time.

UK wiring regulations have required testing of, and specified maximum impedances of, earth's for a very long time.
And as the knowledge of the science has improved then so have the requirements, also the ability to test these things has developed allowing them to be tested.

If I recall correctly early versions of the regulations describe test methods which require the electrician to connect a power source of specified capacity and take voltage and current measurements to establish earth impedances.

I've I get chance I'll post some relevant pages from old regs books later.
 
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  • #60
Thanks- I would be interested. Can't believe the US has not thought of this for over 100 years.
 

davesparks

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Is a low earth impedance necessary on TN-C-S and TN-S?
What exactly did you mean when you asked if it's necessary to test the earth rods on TN systems?
I assumed you meant the earth electrodes at the transformer for the N-E link at source and/or the other TNCS electrodes used along the distributing mains.
 
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  • #62
What exactly did you mean when you asked if it's necessary to test the earth rods on TN systems?
I assumed you meant the earth electrodes at the transformer for the N-E link at source and/or the other TNCS electrodes used along the distributing mains.

Do you have earth rods at the service on a TN-C-S or TN-S system?
 

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