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Topic Title: fixed equipment outside, dissconection times.
Topic Summary: LPG tank installation outside
Created On: 18 April 2013 07:56 PM
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 18 April 2013 07:56 PM
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newpower

Posts: 16
Joined: 30 November 2008

Hi everyone
if someone can help please, i have been to look at a job to wire a lpg 1000ltrs tank single phase to the main cu.

it has been moved from a site where it was wired in to a 20A re-wirable fuse via a cable 2.5mm

it has a metal frame around it protection from damage.

Now, looking at table 41.1 states the maximum disconnection times for final circuits not exceeding 32A.
disconnection time stated for tn system 230v is 0.4s.

to achieve the above i need to install rcd.??
also do i have to supplementary bond the metal frame??

it will be used by taxis and buses to fill up on a commercial site.
it will be self serve to fill up.

if someone can shed some light please.

regards
Sid
 18 April 2013 08:06 PM
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perspicacious

Posts: 7032
Joined: 18 April 2006

I'd check my insurance covered hazardous areas before getting any deeper Sid....

Regards

BOD
 18 April 2013 08:23 PM
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newpower

Posts: 16
Joined: 30 November 2008

thanks Bod, never thought of that one, as i seen the tank wired and running in the old site, it seems that a somebody done a diy job on it, wiring it in to a board which contains the old porcelain brown rewirable fuses.
it didn't seem all that. to wire up at new site.

Regards

Sid
 18 April 2013 08:35 PM
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daveparry1

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Why would you need an rcd to achieve an 0.40 sec. disconnection time then?

Dave.
 18 April 2013 08:48 PM
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slittle

Posts: 3374
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I'd be looking at the earthing type of the installation closely too.

Would you want the tank connected to a TNCS supply and sitting outside on the ground. What sort of currents might be travelling through any metallic pipework ?

I'm with BOD on this one :-)


Stu
 18 April 2013 08:48 PM
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newpower

Posts: 16
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hi Dave, if ever there was a earth fault 30mA or grater, then it would need disconnection of supply within 0.40s.
could i achieve this with a mcb? as the mcb is only short circuit protection.

i am confused

Regards
Sid
 18 April 2013 08:54 PM
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newpower

Posts: 16
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hi stu, yes its a TNCS with a measured Ze of 026 Ohms.

Sid
 18 April 2013 09:01 PM
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jcm256

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Vessels above 1 tonne capacity (2200 litres)
All LPG storage vessels above 1 tonne capacity should be permanently bonded to an effective earthing point to prevent the accumulation of static electricity. Generally, this will be achieved via an earthing rod. This earthing point should be located so as to facilitate connection to the bulk tanker via its own earthing/bonding cable before LPG delivery connections are made.
The electrical bonding should be mechanically sound and protected against forseeable causes of damage (no excess wire length, not running across an area required for access, etc). There should be test records to prove that the bonding point is effective. Tests should be frequent enough that the earth continuity is unlikely to be lost between tests. Tanker drivers should perform a visual check of the installation, including the earthing point, before commencing offloading.
Vessels up to 1 tonne capacity
As an alternative to the above method, a bonding connection may be provided on the tank itself to which the bulk tanker can directly connect its earthing/bonding cable before LPG delivery connections are made. Ideally, the bonding connection would be a dedicated brass or copper stud, but may be provided via a lifting lug or leg. In any case, it must be a corrosion-free and unpainted metal part via which the bulk tanker can achieve a secure electrical connection.
Where there is no evidence that a bonding clamp or other engineered electrical bonding means can be used effectively (e.g. clamp marks on thick paintwork or plastic parts etc.) then an Improvement Notice should be considered. A dedicated equipotential bonding connection point should be provided which can be proved as providing a good electrical connection with the tank. This should be accessible, and maintained free from corrosion which may impair its function.
Buried or Mounded Tanks
A bonding connection providing bare metal contact with the bonding cable from the LPG road tanker should be attached or connected to the vessel.
Buried earth rods should not be used or connected to buried or mounded storage vessels using cathodic protection, either for electro-static dissipation or for the earthing of electrical equipment. Electric pumps should be earthed through the electric supply system.
Earthing Requirements
Site earthing is required for all sizes of storage vessel when fitted with electrical equipment, with the primary requirement being protection against electric shock. The earth should be adequate to ensure that electrical protection devices operate in the event of a fault. BS 7671 provides guidance on this. Test reports should be available for inspection. This is not the same as the equipotential bonding required for the dissipation of static electricity.
References & Further Information
More detailed information can be found in:
Section 5 of the UKLPG Code of Practice 1, Bulk LPG Storage at Fixed Installations; Part 1: 2009: Design, Installation and Operation of Vessels Located Above Ground; Incorporating Amendment 1 May 2012 and

Disclaimer: You need to follow electrical guidance in the apea blue book., (and you know quite well TNCS is not allowed at a hazard area).

http://www.apea.org.uk/publica...ue-book-hardback-copy

Now this will happen in these high cost of living times.

http://www.calor.co.uk/about-c...ling-at-autogas-sites/
 18 April 2013 09:06 PM
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perspicacious

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I thought the trick was to fill up your LPG vehicle from your domestic CH tank to avoid road fuel duty and 15% of VAT........

Regards

BOD
 18 April 2013 09:17 PM
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newpower

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hi that's quite informative.

this customer wants to move the tank from one yard to the other its not fuel thats sold to members of public, this company uses it to fill up there own taxis and mini buses about 150 vehicles, due to expansion they are moving to a bigger place, its a customer i have done other electrical work for and did not want to turn it down.

Sid
 18 April 2013 10:28 PM
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AJJewsbury

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hi Dave, if ever there was a earth fault 30mA or grater, then it would need disconnection of supply within 0.40s.
could i achieve this with a mcb? as the mcb is only short circuit protection.

I think you might be muddling up a couple of different requirements there.

The tabulated disconnection times (e.g. 0.4s) are for faults that make exposed-conductive-parts live - the current that then flows is only restricted by the impedance of the supply and circuit L and c.p.c. (Zs) - so normally a very large current flows (hundreds or thousands of amps in a TN system) - and usually MCBs and fuses can open easily in the required time.

In systems with a large earth impedance (e.g. TT) the fault current will be much smaller - but still typically a lot more than 30mA - so often RCDs are needed - although not necessarily 30mA ones - 100mA or even 300mA RCDs are often used to provide ADS for shock protection under fault conditions (or indirect contact as it's sometimes known).

30mA RCD protection is for a different situation - one where someone might come into contact with a live conductor directly or normal ADS can't be relied upon - and is only demanded in some situations - either where there is a higher risk of shock (e.g. bathrooms), where unarmoured cables risk damage by metal cutting tools, nails etc (e.g. ordinary cables concealed in walls) are or where loop impedances can't be controlled so normal ADS won't necessarily work (e.g. unknown appliances and extension leads plugged into sockets).

MCBs (and fuses) also normally provide overload as well as fault protection.

As others have suggested PME (TN-C-S) supply to outdoor metalwork as a number of significant safety disadvantages and would normally be avoided even under normal circumstances - lots of flammable gas should make you even more wary. For comparison, using a PME earth with petrol filling pumps is entirely forbidden.

If you convert to TT, the 0.4s and 5s disconnection times reduce to 0.2s and 1s.

- Andy.
 19 April 2013 01:38 PM
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newpower

Posts: 16
Joined: 30 November 2008

Andy very well explained mate,

Does this mean its a no go or changing it to a TT would do the job.
if i was to stick a earth rod in, carry out a Ze test to make sure the earth path is suitable as already im getting Ze at 0.26.
if i can bring it down even more and bond all the exposed conductive parts back to the met also put the LPG tank on its own RCBO type C with 30mA earth leakage protection.
after all the above i get Ze 0.20. 230/0.20 =1150A
RCBO type C 20A, instantaneous over current trip is 200A.
the tank is quite close to the main cut out so distance wont be a factor.

so if ever there was any currents flying around the frame 30mA or greater, i assume this condition would be picked up by rcbo.

the thing now is have i completely lost it or is the above possible.

please comment

Sid
 19 April 2013 02:10 PM
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AJJewsbury

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Others here have more experience of LPG etc - so see what they say. My gut reaction would be not to use a PME (TN-C-S) earth.

The problem with PME is that they don't really give you an earth connection, but a connection to their N, which is in turn earthed. This has a number of disadvantages when you've got outdoor metalwork:

1. Because the supplier's N is normally carrying current, you end up with a voltage along its length (usual Ohm's Law stuff), so the MET ends up at a higher voltage than true earth - perhaps by as much as 10 or 15V. If you're inside a building with insulating walls & floors and good bonding, that's not really a worry. If you're outside in contact with bonded metalwork on one hand and true earth on the other (or more likely foot) and things are a bit damp, you might feel a bit of a tingle (usually called 'perceived electric shock'). Of itself it's not dangerous (i.e. the current won't kill you), but it can still have serious consequences if it results in someone jumping back and so falling off a ladder or into the path of something moving. It doesn't do your reputation as an electrician any good either.

2. As the N and MET are bonded together at the intake position, any earthed metalwork you bond forms a parallel path with the supplier's N back to the star point - so you get a proportion of the installation's current flowing back through the bonding (perhaps some of the neighbour's N current too). Note this isn't "leakage" current - no RCD will notice it, but it could be a amp or two and probably not something you want in the vicinity of LPG.

3. Both the above apply during normal supply conditions - PME has one more nasty trick up its sleeve! Should there be any problem with the supplier's N (either a clean break or a loose connection) then the N conductor on the load side of the problem is dragged towards 230V by the connected load. But the load end of N conductor is where your PME "earth" terminal is connected - so that goes towards 230V too, together with your outside bonded metalwork. So you could be outside with 230V across your body with no automatic disconnection at all, and many tens of amps flowing through the metalwork. Breaks in supplier's N are rare - perhaps negligibly so in all-underground networks, but quite a few problems have been reported with overhead distribution.

- Andy.
 19 April 2013 02:32 PM
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OMS

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Don't even think of leaving it as a PME system - repeat - NO PME

start with a TT system, usually at the source end.

I suspect you'll almost certainly need a fire fighters isolation switch - what have the clients asked for - have they informed the LA of the installation

provide 30mA RCD protection

Ensure the tank has a robust connection to an electrode - nothing to do with system earthing

determine if you have any zoning issues and need to use atex equipment for cable glands etc

My advice - don't get involved - you are almost certainly not insured for this type of installation - and if it goes wrong, you might just be the last man standing - so make sure you have the means of defending your actions, if you proceed

Regards

OMS

-------------------------
Failure is always an option
 19 April 2013 04:14 PM
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newpower

Posts: 16
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Hi everyone got some info,

phoned the nic helpline: explained the hole scenario then was told,
the tank does not need any extra earthing as long as its on concrete slabs keeping it away from the mass of earth, to reduce circulating currents or high potential.

what i don't understand is he seemed so relaxed about it and the rcd bit i had to throw in, then was told ohh yes that would be even better.

its been since yesterday im trying to get to the bottom of this.

i was beginning to believe its the end of the road and lost confidence in RCD's and start refusing work in this time of downturn.

Sid
 19 April 2013 04:52 PM
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Legh

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phoned the nic helpline: explained the hole scenario then was told, the tank does not need any extra earthing as long as its on concrete slabs keeping it away from the mass of earth, to reduce circulating currents or high potential.


I thought that you needed to be a registered 'liquid license' holder as well as being on a recognized list with the local fire brigade.

Legh

-------------------------
Why do we need Vernier Calipers when we have container ships?

http://www.leghrichardson.co.uk

"Science has overcome time and space. Well, Harvey has overcome not only time and space - but any objections."
 19 April 2013 05:09 PM
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jcm256

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Did you tell the nic that there was a LPG pump attached to your tank?
Auto gas now incorporated into the blue book, which is a statutory document; you will either leave it to contractors who do hazard installations, or get the blue book from library.
What mad man wired the existing setup in twin & earth, make sure yours comply with statutory requirements. The above advice was good from Mr AJ and Mr Oms, you can see some of it here below. RCDs, Emergency isolation double pole switching etc. (but get the up to date blue book).

http://www.energyinst.org.uk/c...tricalInstallation.pdf
 19 April 2013 06:33 PM
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newpower

Posts: 16
Joined: 30 November 2008

well guys more info,

1) distance needed 3M from any form of switch, any drain and ignition.
2) fireman's switch 3M or exceeding.
3) on its own RCBO.
4) standing on concrete slabs.

i am only responsible for the electrical connection.

'i might think of the lightning electrodes as well on either side of tank'

Sid
 20 April 2013 09:47 PM
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jcm256

Posts: 1792
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New power it is unlikely that this auto gas tank privately owned. They usually belong to the gas company, who supply and maintain them, so do not be going boring holes anywhere without their permission. Please do not take offence but there so many rules and regulations with even the simplest bit of work that you are carrying out, it is not worth it trying to do it on your own. The Project Design Engineer for this site should be involved rather than someone just saying asks the electrician to hook up this gas-dispensing pump.
Signing off, on this thread as statutory regulations are involved, but all the best and looks like you are doing your best.
Regards
jcm


Here is some Important Advice - OWNING YOUR OWN TANK
http://www.uklpg.org/advice-an...o-switch-lpg-supplier/
 22 April 2013 02:12 AM
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newpower

Posts: 16
Joined: 30 November 2008

http://www.ebay.co.uk/itm/LPG-...T&hash=item3f244bc8b9

Hi all the URL above leads to a tank for sale on ebay check it out, it seems that any body can buy a tank and stick it in there garden running on a 13A power supply, it is similar to the one that this client wants wiring up to mains.

what i cant get round that there's so much regs surrounding the issue and there's tanks including the vehicle filling attachment for sale on ebay for people to DIY.

Cannabis cultivation is an affence, and yet you can buy all the equipment including the seeds off the counter but you cant grow it.

thanks for the link to information Jcm.

anyway guys thanks for all the advise much appreciated.

Sid
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