touch voltages 50V and 25V

pushrod · Apr 2, 2011

anyone tell me where in BS7671 it says what touch voltage is allowed for which special location - looked in individual special locations but can't see any mention

cheers.

MarkieSparkie · Apr 2, 2011

411.5.3 applies universally now, Ra x Ideltan <= 50V where 50V is the maximum touch voltage. Pre 17th Ed BRB that equation <= 25V applied to certain special locations, eg. Construction Sites and Agricultural & Horticultural Premises.

IQ Electrical · Apr 2, 2011

The forthcoming new amendment on medical locations sees the reintroduction of the 25 Volt touch voltage.

pushrod · Apr 2, 2011

IQ Electrical said:
The forthcoming new amendment on medical locations sees the reintroduction of the 25 Volt touch voltage.

Do you know which locations it will apply to IQ ?

MarkieSparkie said:
411.5.3 applies universally now, Ra x Ideltan <= 50V where 50V is the maximum touch voltage. Pre 17th Ed BRB that equation <= 25V applied to certain special locations, eg. Construction Sites and Agricultural & Horticultural Premises.

Hi Markie , yes quite a few references to 50V in brb and i was always under the impression that several special locations like the ones you mentioned were limited to 25V but i can't actually find it written in there

Just can't remember if i have seen it written down or whether it has been people thinking of the 16th have been telling me.

IQ Electrical · Apr 2, 2011

pushrod said:
Do you know which locations it will apply to IQ ?

Hi Markie , yes quite a few references to 50V in brb and i was always under the impression that several special locations like the ones you mentioned were limited to 25V but i can't actually find it written in there Just can't remember if i have seen it written down or whether it has been people thinking of the 16th have been telling me.

Yes, there is a new 'zone-type' system introduced on medical locations, the zones being called 'groups'.

The groups are numbered from 0-2 where 0 is the least 'intrusive' area eg. examination room/massage room and 2 where intercardiac procedures are performed and loss of supply can cause danger to life.

The 25 Volt touch voltage is introduced for groups 1 and 2 along with a new disconnection time for 230V Uo circuits of 0.3 Seconds (TN systems) and 0.05 Seconds (TT systems).

There are no other incidences of the 25 Volt touch voltage in BS7671:2008 or amendment 1

malcolmsanford · Apr 2, 2011

IQ Electrical said:
Yes, there is a new 'zone-type' system introduced on medical locations, the zones being called 'groups'.

The groups are numbered from 0-2 where 0 is the least 'intrusive' area eg. examination room/massage room and 2 where intercardiac procedures are performed and loss of supply can cause danger to life.

The 25 Volt touch voltage is introduced for groups 1 and 2 along with a new disconnection time for 230V Uo circuits of 0.3 Seconds (TN systems) and 0.05 Seconds (TT systems).

There are no other incidences of the 25 Volt touch voltage in BS7671:2008 or amendment 1

Bet there is a waiting list for your GP mate.......................

Engineer54 · Apr 2, 2011

Looks as if BS7671 is adopting the German DIN VDE 0107 for hospital medical rooms. Which uses the same group designations as stated above. The German system is basically recognised as the international standard for electrical installations in hospital medical rooms/locations etc...

It'll be interesting how much of DIN VDE 0107 they actually incorporate?? There's quite a bit involved in the design side, let alone on the installation side of things...

This is the Standard i've worked too, on virtually all of my hospital projects, and is far superior to the present UK set-ups.

malcolmsanford · Apr 2, 2011

Engineer54 said:
Looks as if BS7671 is adopting the German DIN VDE 0107 for hospital medical rooms. Which uses the same group designations as stated above. The German system is basically recognised as the international standard for electrical installations in hospital medical rooms/locations etc...

It'll be interesting how much of DIN VDE 0107 they actually incorporate?? There's quite a bit involved in the design side, let alone on the installation side of things...

This is the Standard i've worked too, on virtually all of my hospital projects, and is far superior to the present UK set-ups.

So gone are the days of ...............well stick either an IMD or more commonly an RCM on it and let the lights buzz then, I always found how deaf people were even with a 80Db audio alarm going on.

Yes did quite a lot of Phillip Holztmann work here in the 90's using the german standards, though I loved the copper work for the MRI unts. or when the cleaners come in with metal buckets.