300mA RCD question

[raithrovers1]

Gents

Can anyone give me the standards and justifications for fitting a 300mA RCD for the purpose of fire/ equipment protection.

I have a UPS on site with all the loads fed from 300mA RCD's. I have never come accross this before and problems have been rearing their head with RCD's tripping on in-rush etc. We want to remove the RCD's. The UPS is old and the site has changed ownership. Documentation can not be found as to why the 300mA RCD's were spec'd in the first place.

Any help would be appreciated.

 

[malcolmsanford]

300mA RCD are utilized in locations that are at risk of fire due to stored materials say or processing operations, a good example is farms. These are used to protected against insulation faults and it is regardless of the earthing system be it TN or TT

There are a few exemptions for omitting RCDs such as the use of MICC cable.

The relevant part of the regs is 422.3.9

 

[i=p/u]

the houseim working on at present has old 3036 board but you can see recently someone has jammed in 300mA rcd/powerbreaker in the tails before cu.. and this is a a tn-s, and i thought were only for farms /tt systems

 

[malcolmsanford]

the houseim working on at present has old 3036 board but you can see recently someone has jammed in 300mA rcd/powerbreaker in the tails before cu.. and this is a a tn-s, and i thought were only for farms /tt systems

When you say recently how recently? Could it be an old ELCB?

Often if there is a breakdown or replacement of a cable from the DNO you can find that a Ze value on a TN-S system can rise and give concerns about the ZS values and achieving disconnection times. Often then an upfront RCD would be installed to provide additional protection.

The reason I ask how long as this been in is that often the DNO would fit these as a "temporary fix" while work was being done, and you will find quite a few old TN-S installations with these knocking about.

 

[raithrovers1]

Now I have two problems:
1. The UPS is on an Oil & Gas installation and the 17th edition does not apply out there! After reading the regs (422 Precautions where particular risk of fire exist) it would seem that that it does apply to sites like farms and mills as malcolmsanford states where setting light to combustible materials may occur.
2. After some investigation I have found the following. A 300mA RCD is used to limit a conductor fault wattage to below 60W which is considered the amount of power required to start a fire. All of my load circuits pass through modules which have the potential to have gas ingress. I would imagine that 60W is enough to ignite a flammable atmosphere. Therefore are these 300mA RCD's serving any purpose?

 

[netblindpaul]

Perhaps you need to be checking the guidance with regard to DSEAR?
ATEX/COMPEX may be a good place to start?
I am surprised that you are working on flammable atmospheres equipment without being "COMPEX" trained & certified?
I would be tempted to check your insurance cover as it may exclude DSEAR areas.

I may have the wrong end of the stick though!

 

[raithrovers1]

"I am surprised that you are working on flammable atmospheres equipment without being "COMPEX" trained & certified?
I would be tempted to check your insurance cover as it may exclude DSEAR areas."

I am compex certified but this not a specific hazardous area problem. The UPS is in a safe area. The equipment it feeds is either in a safe area or in ATEX approved enclosure. The only problem may be that the cables run through hazardous areas.

 

[netblindpaul]

OK, then there should be requirements on this from the COMPEX/ATEX side?
If not what's the issue?
I don't quite follow?
You say 7671 does not apply?
You are OK with the COMPEX/ATEX stuff, so I don't quite get the issue?

I'm not "having a go" so please don't think I am, hence the "wrong end of the stick thing" in my last post and please read the same in this one, I am just trying to understand what you are looking to do/for.

What are you trying to protect with the RCD's or is this the crux of the Q?

What does the original install information say?


The UPS is out of zones, the current consuming equipment is out of zones?
Yes?

 

[raithrovers1]

I realise you are not having a go and I appreciate your comments.

"What are you trying to protect with the RCD's or is this the crux of the Q?"
Yes, this is the crux of the question. We do not have the orginal install information so we have no idea why the RCD's are there in the first place. There seems to be no real justification for them.

 

[netblindpaul]

OK,
Then I suggest you track down the relevant BS's & ACoP's and start trawling, I would certainly NOT remove the RCD's without doing a full design review & RA.
I'm not sure which BS's without checking and the ACoP's will be those on DSEAR from the HSE, you will get further reading in these.

 

[malcolmsanford]

Just come back onto this and to be honest I have not had many dealings with the petrochemical industry or the relating standards, certainly not to the extent of Paul or You RR.

But do agree with Paul that your going to have to be really careful if your contemplating altering the design characteristics of the installation and if removing RCD fault protection for say just MCB, is going to, in the eyes of most bodies, leave the installation not as safe.

As suggested I would be doing a lot of calculating on this and making sure your doing full and detailed risk assessment backed up by comprehensive design figures, just make sure you have all the "i" dotted and the "t" crossed mate

 

[Engineer54]

I realise you are not having a go and I appreciate your comments.

"What are you trying to protect with the RCDs or is this the crux of the Q?"
Yes, this is the crux of the question. We do not have the original install information so we have no idea why the RCDs are there in the first place. There seems to be no real justification for them.

You still haven't given us any idea what loads these RCDs are protecting??

As for these circuits passing through a hazardous area, what is the method of installation?? If any enclosed containment is involved, as in conduit, this would need to be unbroken and gas sealed with a purpose made sealing fittings and sealing compound before and after passing through any hazardous areas.

As for your mention of ''modules'' i'm not sure what you mean by that term? Are you referring to enclosures, if you are and they have the potential for a flammable gas to enter, i'm at a loss!! All enclosures located with hazardous environments must meet explosion proof codes, ....ie ...Any explosion within such an enclosure, should not be able to escape to the general atmosphere, for obvious reasons!!

So can you be a little more specific in what your talking about and enclosure types were talking about too. I must admit, i am far more experienced with American hazardous area spec's than i am with UK/European spec's. I'm also aware that American spec's are far more onerous than our spec's/reg's