Pub Main Fuse

[charliefarli]

Hi all, just thought I would ask some of you experienced sparks out there some advice if I could!

I recently got called to look at a pub which has a single phase supply with a fuse carrier with 300 amp written on it and it takes the type J style 415volts fuses. I have never come across a single phase supply like this and suggested to them they need a three phase supply as its a 5 story building and they are converting it into a restaurant,bar and offices above. The problem is they do not want to pay for a three phase supply to be installed because of the cost, so have asked if I can use whats there. Would I be able to put a 300 amp fuse in main head and come out of fuse in 95mm tails, and split off in a 300 amp henley block to two 100amp fused isolators in 25mm tails and then there will be 2 x 25mm armoured's going to two separate DB's. I would also run a 35mm earth to gas and water and 50mm main earth. your thoughts on this would be much appreciated as I am a bit confused how to handle this one.many thanks in advance!

 

[Leesparkykent]

Get the DNO involved. But they will probably be looking at a 3phase supply Imo.

 

[telectrix]

from you OP,i'd say that a 3 phase supply is the only way forward. if the client don't want, then walk away and allow a cowboy to set the place alight.

 

[charliefarli]

Thanks for reply Lee. Have you ever come across a single phase supply like this? Its an old pub and the people who own it did call the DNO in to change the fuse carrier because they thought it was old and needed replacing but the guy who came said it was fine for continued use.

 

[davesparks]

You cannot put any fuse in the head, that is the DNO's property and only they may touch it.

You can't just split it in a Henley block, you need to install a main switch for the installation and then your distribution equipment after that or install a panel board with main switch in it.
Why would you run 35mm bonding and 50mm earthing conductor? Is that based on any calculation or just a random guess?

 

[charliefarli]

is it possible to use a single phase supply if its big enough for 300amp? I have never come across it but the fuse carrier and incoming cable are huge and were obviously bought in to take a lot of power. I suppose if i call the DNO and explain what is there and what I am going to be pulling through it they can tell me if its adequate but just wanted to ask people here if they had ever seen same thing before and how they got round it.

 

[charliefarli]

can I not split it in a block if the two 100amp fused isolators are right next to it main fuse?i thought this would be ok seeing as it single phase.

 

[charliefarli]

my earth sizes weren't random guesses but I have not done a calculation, just what I thought would be adequate off the top of my head.

 

[davesparks]

my earth sizes weren't random guesses but I have not done a calculation, just what I thought would be adequate off the top of my head.

So no better than random guesses then!

 

[davesparks]

can I not split it in a block if the two 100amp fused isolators are right next to it main fuse?i thought this would be ok seeing as it single phase.

What has being single phase got to do with it? All installations should have a single main switch regardless of how many phases there are

 

[Leesparkykent]

my earth sizes weren't random guesses but I have not done a calculation, just what I thought would be adequate off the top of my head.

what's the earthing arrangement?

 

[charliefarli]

its TNS, well I suppose earths are a bit of a guess, was just throwing it out there really, sorry wasn't exact. I wish they just got three phase would be so much easier. I appreciate that Dave, The guy reckons 200 amps would be more than enough so going to ring DNO tomorrow and see if they think this will be acceptable for service head thats there.

 

[charliefarli]

if they say its ok, i could put a 200 amp isolator in first and then two 100 amp isolators off this going to dbs.

 

[Andy78]

its TNS, well I suppose earths are a bit of a guess, was just throwing it out there really, sorry wasn't exact. I wish they just got three phase would be so much easier. I appreciate that Dave, The guy reckons 200 amps would be more than enough so going to ring DNO tomorrow and see if they think this will be acceptable for service head thats there.

Don't you think a maximum demand calculation based on the proposed building alterations would be more appropriate for the purposes of supply sizing than what some guy reckons ?

 

[davesparks]

its TNS, well I suppose earths are a bit of a guess, was just throwing it out there really, sorry wasn't exact. I wish they just got three phase would be so much easier. I appreciate that Dave, The guy reckons 200 amps would be more than enough so going to ring DNO tomorrow and see if they think this will be acceptable for service head thats there.

Why on earth would you want a 35mm main bond on a TNS when the maximum for is 25mm?

What 'guy' reckons it needs 200A? A qualified and experienced electrical consultant?

If it's a 300A SP supply and you need 200A I really don't see what is so difficult? Why would three phase be easier when there's already a large SP supply! Surely it's easier to use what's there already than install a new supply

 

[davesparks]

if they say its ok, i could put a 200 amp isolator in first and then two 100 amp isolators off this going to dbs.

Isolators are no good, you need either switch-fuses or fused-switches to feed the distribution circuits. Or else you could install a panel board

 

[charliefarli]

I have to hold my hands up and say I am not to experienced with this kind of single phase arrangement, and just wanted to ask some advice. Sorry if I am annoying you with my quotes and questions but I really do appreciate all your replies.

 

[charliefarli]

i meant fused switches when I said that apologies. That would be ok take it?

 

[Stu1312]

What type of metering is onsite? If it's a single phase whole current meter the maximum it will take is 100amp so you will just fry the meter if you up the fuse size.

 

[davesparks]

I have to hold my hands up and say I am not to experienced with this kind of single phase arrangement, and just wanted to ask some advice. Sorry if I am annoying you with my quotes and questions but I really do appreciate all your replies.

If you are not experienced with single phase then what are you experienced with?

 

[Hobsoni]

Bit Harsh

 

[Sparkie30]

People dont hold back these days mind you.

 

[Martin Kerr]

Hardly a typical single phase arrangement also , the first thing OP needs to clarify is what size of supply is actually available to the installation, just because there is a 300a fuse carrier at the origin, doesn't mean it's all available.
Then he needs to verify his maximum demand, to see if the original single phase supply is adequate for his needs

 

[davesparks]

Hardly a typical single phase arrangement also , the first thing OP needs to clarify is what size of supply is actually available to the installation, just because there is a 300a fuse carrier at the origin, doesn't mean it's all available.
Then he needs to verify his maximum demand, to see if the original single phase supply is adequate for his needs

What's not typical about it? The arrangement is not going to be any different to a 100A supply other than a bigger cable.

Everything you describe about checking the suitability of the supply is the same regardless of what size supply or how many phases there are.

 

[Martin Kerr]

It is not a typical single phase arrangement ,if the supply could be in excess of 200a,which would then require a sub distribution system to feed a DB arrangement ,depending on the installation network over the 5 floors
The advice to the poster was not to check the suitability of the supply ,but to check the maximum supply available ,as the only indication as to the max supply available was the 300a fuse carrier, only when this info was obtained could you begin to evaluate if the original supply was adequate for the installation needs

 

[PEG]

I read "restaurant,bar and offices..." and immediately thought the starting point of this should be an assessment of requirements.

 

[shanky887614]

get a bubar chamber then switched fuses off it if you dont want to go down the route of a board

 

[Darkwood]

Reading through this thread, I'm a little concerned here that although a little advice was asked for it would appear a lot of advice is needed and with no disrespect to the OP who may be very competent within his comfort zone, this is not in his experience and I strongly suggest he either passes the job on or more favourably, gets a firm in and works alongside them so as to gain the invaluabe experience.

The descriptions would have me believe that the design of the distribution end of this install is a critical stage and any errors could be costly to businesses within the property, then the legal games would begin.

Firstly would be to find out who is paying the Electric bill and get the details and then enquire about KVA allowance for the premises, this is the first stage key step.

If their is a 300Amp 1ph supply available and the calculated demand is below this with room to move then their is nothing wrong with using it and no need to start telling customers they need 3ph supply. In an Ideal world a 3ph supply is a nice option if available in such circumstances, the problem now is the customer has been fed possible incorrect info' stating requirements of 3ph before any enquiries have been made and will only give the impression to the customer that he doesn't know what he is doing if it transpires the existing is adequate, this could lose what sounds to be a nice little contract.

I not too happy that this thread now seems to be taking a turn in trying to suggest how to design the front end distribution as we are not here to give a step by step design guide.

@ The OP - by your own admission, you are not experienced in this area (thankyou for your upfront honesty) and quite rightly you are looking around for advice on the matter, but I would suggest this isn't about just getting a few tips on the matter and actual needs careful design, I would not recommend this over a forum as simply missed snippets of info can be a game changer in the design and thus I would recommend you get a company in to design and install the distribution side while you do the rest, both learning from those doing the work and keeping the main contract for yourself; (where your experienced I assume and well within your comfort zone).