immersion heater and a shower pump

[Deleted member 26818]

Unfortunately the OSG and the guides are not actually written by the same people.
They may be published by the IEE, but they are not as the engineer says BS7671.

 

[tonys]

strikes me as a bit of an arrogant attitude by the engineer.

NICEIC Engineer, the type who was blunt, no kid gloves, no skirting about the edges, told you how it was, if you carried out a PIR and got anything wrong, you were told straight.

Today all the schemes are soft imo someone like the above would assess you hard and break people who were not up to the task.

 

[Deleted member 9648]

I take your point that there seems to a discrepancy here. My own feeling is that it(reg 554.3.2) dates back to pre 17th where you would expect there to be supplementary bonding on the pipe work and that it has not been updated to go with the fact that installations to the 17th edition, with circuits under the control of RCDs, no longer require supplementary bonding to metallic boiler pipework. ??

If not i still ask where are the immersion heaters that these regs apply to?

Also, i think "uninsulated element" is not referring to the resistance wire not having insulation around it, but to the fact that there is no insulation around the outer metal case of the heating element.

It would be interesting to get a few more opinions, maybe someone like widdler or IQ.

I agree that these bare heating elements appear to be somewhat mythical...I cant answer that one...but there does seem to be conflicting requirements here....
And yes it would be useful to hear some views on this from some of the other members on here.

 

[tonys]

Stop Press: Immersion element construction update.
I've been in contact with half dozen leading manufacturers of domestic and industrial immersion elements this morning.
It appears air insulated elements are 'old school' and rarely manufactured today and silica insulated elements are reserved for the budget end of the domestic market.
In order to achieve higher wattage densities, thermal efficiency, maximum electrical insulation, hot spot reduction and long life the insulation material most manufacturers currently use is compacted refractory magnesium oxide (MgO) in both domestic and industrial immersion heaters.
Summary:
Electrical manufacturers confirm domestic immersion elements are of insulated construction and that the 554.3 group of regulations do not apply to their products. Heatrae Sadia and Santon going further, stating that the 554.3 applies specifically to shower and quick-boil instantaneous water heaters.

You would of thought the manufacturers of all people would know their own products ?

 

[IQ Electrical]

Wow, what an interesting thread!

There are so many variables here that it's difficult to find a black and white answer!

1 I believe the domestic type immersion heater to be insulated.

2 Guidance Note 1 does indeed stipulate that 'immersion heaters should not be connected by a plug and socket outlet but by a switched connection unit complying with BS 1363-4'

3 Guidance Note 2 refers to regulation 554.3.3 as applying to "water heaters having immersed, uninsulated elements"

4 Table 3.1 classes even an unswitched plug and socket outlet to BS 1363-1/2 as a device suitable for isolation.

5 Have a read of the following link and before anyone mentions it, I know it's a 16th edition commentary but the terminology certainly hasn't changed and it illustrates the definition of an uninsulated heating element as opposed to an electrode boiler perfectly!

Commentary on IEE wiring regulations ... - Google Books

 

[Deleted member 26818]

That would appear to clear that up.

 

[tonys]

That would appear to clear that up.

Would like an opinion from Engineer 54, before this can be put to bed lol

 

[Deleted member 9648]

IQ's link appears to confirm that GN1's ref to 554.3 for household immersion heaters is somewhat inaccurate.

 

[Deleted member 26818]

That's the problem with the GNs, sometime's they are inaccurate, and they often contain information from old no longer in use Regulations, and also from sources other than BS7671.

 

[tonys]

That's the problem with the GNs, sometime's they are inaccurate, and they often contain information from old no longer in use Regulations, and also from sources other than BS7671.

That's why I always refer to BS7671, that's the one we work too and test and inspect too and appears on all our Certificates.

Books like the IEE Electricians Guide to the Building Regulations should not offer codes for PIR's, because its not for the purpose of test and inspection work.

A mate of mine phoned the IEE about it and they told him the codes for PIRs should not really be in the book.

 

[pushrod]

An immersion heater on a plug top - not allowed as should be on a switched connection unit to BS 1363-4. What code would you give it ? and out of interest what is the thinking in not allowing it as a plug and socket would give double pole isolation?

Also would a shower pump be allowed on a plug top? Plus it is on the same circuit as the immersion. My initial thought was that the pump could be on a plug and socket but should not be on the same circuit as the immersion

cheers.

Well in actual fact pushrod an immersion heater with a standard metal sheathed element can be on a plug top. I know you will say what about reg 554.3.3 and GN1 but they are referring to a different type of immersion (one that has an uninsulated element, not very common in houses for heating large volumes of water ).

Also 8.5 of the OSG is not being specific when it talks about immersion heaters being on a connection to BS1363-4. Both should really be less vague. The only reg that is directly applied to standard metal sheathed elements is 554.2 that they have, or are provided with, an automatic cut out to prevent overheating.

So you don't need to give it a code at all

Think you are just about spot on with the second part of your OP.

BTW many thanks to all who have contributed especially IQ who must have waded through the whole thing in one go! and gave the vital link; and tonys - obviously very little can substitute for experience
[just my luck to remember the vague references in guides!!!]

 

[MarkieSparkie]

Harrah!
We have a concensus of opinion that the only specific Reg applicable to domestic insulated immersion heater elements is 554.2.1
Aside:
Just got my copy of GN1 today (to check the text you guys were quoting) 'GN1 8.2 water heating' does, as stated apply to uninsulated immersion elements and references the 554.3 group of Regs, but I think IQ and others have proved, ex silentio, that Gn1 8.2 and this group of Regs do not apply to domestic insulated immersion heater elements, the subject of the thread. Likewise GN2 4.5.4 does not apply for exactly the same reasons.
Markie throws big spanner in the BS1363 argument:
Just been looking at the BS1363 Standard that applies to 13A accessories, an absolute maximum ambient temperature of 40 degrees Celsius applies. Also, Clause 2a of the document states that 'the environmental ambient temperature must not average >25 degrees Celsius in any period of 24 hours'. Clause 2(b) says that it does not cover 'a situation subject to exposure to direct radiation from the sun or other sources likely to raise temperatures above the limits specified in a)'
So the FCU or plug/socket is suitable for "hot days" in summer as long as the absolute maximum ambient temperature limit is not exceeded. However, if the FCU or plug/socket is in an airing cupboard and the tank contains water at 60-80 degrees C and in summer the ambient temp in the house is >20 deg C, it stands to reason that both the absolute 40 degrees C and the 24 hour average of >25 deg C may well be breached?
So in my opinion that excludes BS1363 accessories from use in an airing cupboard or similar enclosure.

 

[tonys]

Good post Pushrod

 

[pushrod]

Good post Pushrod

Or maybe not, now that MarkieSparkie has posted lol

My own immersion isolator (dating back 40+years) is on a DP switch outside the airing cupboard - the guy who did it must have known


(runs to get max-min thermometer out of greenhouse... not!)


EDIT : so would you code the plug top in the airing cupboard MarkieSparkie?

 

[MarkieSparkie]

Well pushrod from what we now know, all BS1363 accessories in an airing cupboard would be working close to their maximum current rating, so once we breach either of the temperature ratings we have in effect a potential overloading of the accessory, so the answer has to be a definite yes, Code 2.
If however the accessories are outside the airing cupboard then maybe yes, Code 2.
I say maybe yes, Code 2, because I'm still concerned about potential overloading, there is so little headroom on the maximum current (13A) rating of BS1363 accessories in this situation. Putting my 'designers hat on' the worst case condition to be considered in normal circumstances is when the supply voltage rises +10% from nominal and we are again overloading the accessories, if water is being draw off regularly this situation it could potentially be for hours at a high duty cycle.
I think on balance, my personal view either as an inspector/tester or designer, I'm against BS1363 accessories in this situation and will specify a BS EN 60669-1 20A DP Control Switch and justify my decision (Code 2, potential overload) to all.
In other circuits and situations we could apply a derating factor to the accessory at the design stage and all would be fine.