TOUCH VOLTAGE

[steptoe]

why would you use a guide when there is a perfectly good reference book avail.able in the BS 7671 document?

thats almost like saying I dont know what sort of paint to use, I'll go by the label on the tin, oh goody, its black paint, that will do.

 

[SPECIAL LOCATION]

Oh dear, no one knows how to calculate touch voltage.I'll set you all an task, then we will see what sort of touch voltages can be present where 415 is not utilized and the designer hasn't specifically designed for a certain touch voltage, I'll use the circuits within the onsite guide---------- Post Auto-Merged at 00:08 ---------- Previous post was made at 00:06 ----------

Humble pie anyone?

NO...

use a circuit from a general installation that is NOT within the scope of the OSG.....

That is NOT supplying a special location.....

Or do they not exist???????

 

[park1]

Ok

 

[Manator]

OkUt = If R2

Ut is the touch voltage, this is assuming bonding is in place and within a protected zone.

Let's assume a fault current of 4 ka.

Apply that to a few R2 impedance of some circuits in the onsite guide and see what touch voltage you get.

Now as I said, we are omiting 415, it's not required.

---------- Post Auto-Merged at 00:22 ---------- Previous post was made at 00:17 ----------

Specs you can apply it to any circuit, if 415 is not being used unless you design purposely to achieve a certain touch limit it will be governed by Ut= If R2.

I doubt many of you would no how to design a circuit to ensure a 25 volt touch limit.

I have to do that on a daily basis, in fact some regulations I work to require an even lower value.

 

[park1]

I have to do that on a daily basis, in fact some regulations I work to require an even lower value.

Then you of all people should know you don't get a 50 v touch limit or less by default. Maybe GN 5 is wrong, what would Mr cook know, maybe IEC 60479-1 is wrong too?

 

[Manator]

Sparc, I am finding it increasingly difficult to understand where you are coming from. Most members here will tell you I am one of the more relaxed moderators, in fact laid back so far that some accuse me of being asleep.

Your above statement is indeed flawed, during the transfer to the 17th edition there was some confusion with touch voltages, with some engineers interpreting the new regulations to allow a touch voltage of 230v. I refer to the IET forums 26th February 2008 "17th edition touch voltage".

Regardless of what you think, touch voltages are to be considered within the whole installation and not just parts there of.

 

[Smilers]

As Manator has stated spark the big green book that your reading out of was partially written by the person you are arguing with- I predict that you wont catch him out !!

Generally when some of the forum members that have a very good grasp on this subject eg Manator, Brian, sidey, boatboi and deke etc etc spec-loc the most appropriate response is shut up and listen.

If nothing else you can see they have considered answers and that coupled with a sound knowledge of our industry and years of experience means you wont win an argument on this topic.

They wont say black because your saying white so admit defeat and go back re study your regs book because I think you may be misinterpreting some of the content.

 

[park1]

As i said in general requirements there is no specific limit in touch voltage prove me wrong im still waiting.....

I'm am referring to protection via Ads.

 

[Steve3948]

Ze = 0.05, Jesus is the house built on top of the transformer.

 

[park1]

Manator

Just looked at the IET thread, oms who is a consultant, and others are stating exactly my point. Only RR disputes it, though I disagree, for one you wouldn't use the tripping current but the peak cut off current for a MCB. I would read the thread again.

lol, Steve, well if we assume a maximum of 16 ka for a domestic then it's even lower, although it doesn't need to be that high. The more stiff the supply the greater the voltage dropped accross R2

 

[Manator]

Manator its quite simple really.If you design to the general requirements of BS 7671 it does not place a specific limit on touch voltage. You and nobody else have proven otherwise. 415 is additional protection, and special locations aside you show me which regs, im still waiting.....

Example TNCS Ze = .05 Simple lighting circuit, 1.5 twin and earth 50 meters long R1 = 0.725 R2 = 1.1 ZS = 1.875

If= 230/1.875 = 122.66 amps Ut = 1.1 x 122.66 = 135 volts

Oh look at that a touch voltage greater than 50 Volts, yet my design meets all the general requirements of BS 7671.

As i said in general requirements there is no specific limit in touch voltage prove me wrong im still waiting.....

Oh and why even have 415 if by default we obtain a touch voltage of 50 volts or less.

Im afraid people on here, if they dont understand they are rude and patronising and then wonder why people dont help and sod off to another forum, mods included.

I have shown you a worked example which meets the General requirements of BS 7671, now you prove me wrong!!!

Care to elaborate how this example meets all the requirements under BS7671, I have already proven you wrong but you have refused to notice.

 

[park1]

Well we're talking shock protection.

Using the above example.

So I'll use Ads as my choice. Disconnection times are met, I have a protected zone and all extraneous parts are bonded. So I think you need to elaborate as to how I have not complied with shock protection, are you suggesting ads fails reg131? If you are correct then pretty much most of the circuits in the onsite guide will fail bar TT and pretty much most circuits using ads.

As yet you have failed to show me, I await a clear explanation.

Thanks

 

[Manator]

Are we talking about ADS or touch voltages? Are you moving your argument based on what you know or think? The OP is definitely about touch voltage, which is why my initial comments on the regulations above started at the beginning of the book.

A sweeping statement that touch voltages are only intended for special locations is clearly wrong under those regulations.

 

[park1]

Don't you think they go hand in hand?

Its a misconception that touch voltages are limited to 50 volts or less. I given you an example, using ads for shock protection and the touch voltage is greater than 50 volts. I think I've been quite clear.

So can you elaborate on where my design falls foul of BS7671, if it does then you are saying that Ads is not sufficient for means of shock protection, I am still awaiting your explanation.

Please read my previous posts, they are quite clear.

Thanks

---------- Post Auto-Merged at 20:23 ---------- Previous post was made at 20:19 ----------

Manator you asked me to elaborate how my design meets other aspects of be 7671, so I have using Ads, so I'm not moving the discussion, you did, I elaborated. You have yet too!!

Thanks

 

[Manator]

OK in a step by step guide:

Do they go hand in hand? My answer NO they do not, each are examples of compliance with the regulations.

Your design made no comment on the protective devise, just a circuit lay out which clearly would not comply to the regulations.

Now you can change your stance, and go on another tangent if you like but the fact remains I am right! Touch voltage should not be confined to special locations but to the whole installation, which is what your argument was based on.

Regurgitating calculations and ADS times as absolutely nothing to do with touch voltages.

Just for clarity so that you know, ADS is one method of complying with the regulations I stated. However I never thought we were talking about ADS I presumed by the Title we were talking about touch voltage.

I love edits, I like the fact that they sometimes run soooo late that you are felt wondering why did I do that!

 

[Sharpend]

Ze = 0.05, Jesus is the house built on top of the transformer.

I should ask $park that question, Jesus gave up house building many years ago.

 

[park1]

I accept you can design to limit touch, as you know medical locations, 415 ensures 50 v or less in that location, but as I have stated I can comply with shock protection yet the touch voltage will may be greater than 50 v. You have yet to prove otherwise, and I know you can't

---------- Post Auto-Merged at 20:36 ---------- Previous post was made at 20:30 ----------

OK in a step by step guideo they go hand in hand? My answer NO they do not, each are examples of compliance with the regulations.

Your design made no comment on the protective devise, just a circuit lay out which clearly would not comply to the regulations.

Now you can change your stance, and go on another tangent if you like but the fact remains I am right! Touch voltage should not be confined to special locations but to the whole installation, which is what your argument was based on.

Regurgitating calculations and ADS times as absolutely nothing to do with touch voltages.

Just for clarity so that you know, ADS is one method of complying with the regulations I stated. However I never thought we were talking about ADS I presumed by the Title we were talking about touch voltage.

I love edits, I like the fact that they sometimes run soooo late that you are felt wondering why did I do that!

I agree, touch voltages should be considered through out an installation. I was just pointing out the misconception. Manator most use Ads, certainly on this forum, I doesn't ensure a 50 v touch limit, that's all I'm saying.

 

[Manator]

Like I said the two should not be confused, the regulation clearly state that to prevent injury or death the current passing through the body should be limited to a level that is not dangerous, it also states that it should be limited (by time). ADS is clearly the best method of achieving this, and you comply with the regulations because you have indeed limited the time of voltages above those considered safe to a safe level.

I have to comply like you say to more stringent rules, and even with ADS I still have to show test results for touch voltage graphs. Invasive medical procedures will be even lower, and they are when even I bring in the specialists.

The reason for debate is to discuss, often when I use the phrase argument it is based on the meaning of the word not the interpretation it has come to suggest.

You did put good argument, however I thought it was flawed simply because you did not disassociate touch voltage from ADS, which are two separate ways of designing a circuit to regulation.

I have been a little sarcastic in my replies also, for which I do apologise, I find it unrewarding trying to be smug on such a trivial matter such as this.

You clearly have some knowledge, and it is based on good facts, not everything is black and white and there are ways around the regulations that even I have not tried yet.

 

[park1]

Apology accepted.

The op states touch voltage, I assumed Ads.

Post 2-5 stated 50 v max, I was stating that is not always the case, when using Ads.

Post 6 Spec refereed to 415, this is not applicable to all circuits, and only protects that zone.

Posts 2-5 show the common misconception.

I should of been more clear with my reasoning.

I know there are other ways to meet shock protection. I know you have to design to 25 volts, I understand the design principles to achieve this, it's not a problem, but it's not something I do.

Some members soon pour scourn when clearly they don't understand. It's quite frustrating. I came on here to help other members.

I also apologise.

 

[Manator]

Apology accepted.

I hope now you can see in written form it is so hard to weazle out what is actually intended, we all suffer from the same problem. Face to face you would know exactly what was being said, and how. In written form you are left guessing most of the time.