Maximum Demand Question

[Dairyspark]

Hi guys, needing a wee bit of help with this.

I'm installing a new 3ph board for shore power supplies to the boats that come up the slipway, as we get a varied means of supply it's going to contain the following on each of its own circuit

230v Sockets

1 x 63A

1 x 32A

2 x 16A

400v sockets

1 x 16A 4 pin

1 x 16A 5 Pin

1 x 32A 4 pin

1 x 32A 5 pin

1 x 63A 5 pin

so my question is, can these be diversified to obtain maximum demand?

Thanks in advance

 

[apprentice87]

Depends how many boats are going to arrive!!!!

What is the power to the boats for?? Just because a boat is connected to a 32A supply, does not mean that they will be drawing all that current. What the boats using the power for??

You are going to have to hope that you CAN allow for rather a lot of diversity, as what are you going to power all this from?? That is an awful lot of power needed.... 147kW

What you mean by "Varied means of supply"

john...

 

[NozSpark]

I think understand that different boats require differing types of supply,,,,

but as John says....

How many boats is this likely to supply?

Remember that each socket will need its own RCD protection

 

[Dairyspark]

2 boats at a time and by varied means I meant some have 230v inlets som have 3ph 4 pin etc. So a selection of different outlets is needed

And as for loading it's very tricky, for example, we have a wind farm boat that comes up, uses the 63A 5 pin but only draws maybe 14-15 amps per phase, sometimes but rarely 40A per phase, however at he other end of the scale we have boats that come up that only ask for a battery charger to be used so very low current use.

The Main switch on the board is going to be a schnieder 4 pole RCD

Also the boats usually use power to run lighting, cookers, TVs etc.

The bigger the boat the more home comforts lol

 

[ProDave]

I'm guessing it's not a marina for pleasure craft, at least not the sort I am familiar with.

Strikes me as a little odd, as all the bigger ships usually run their own generators all the time, even when in port.

 

[Dairyspark]

No its a boatyard for fishing boats and work boats, and they can't run their generators as they are out the water on a slipping carriage, so no water to cool the gen set.

 

[Andy™]

i guess it depends on how many will be used together. i.e if only 1 boat can berth at a specific point and you have 3 sockets there for different options, then you could use the value of highest rating then ignore the rest

 

[kerching]

If your max number of boats is 2.....AND the highest anticipated useage is 2X 63 A 5 pin

Then i would think that 2 X 63 A 5 pin would be your max requirement, but as said before, what is the load drawn by these 63A gin palaces

Caveat.....i have been sampling my latest batch of Chilean Merlot ce soir, so I am not thinking or seeing clearly

 

[Dairyspark]

Only one 63A 5 pin lol and one 63A 230v for fishery protection boats that come up for surveys. They are drawing anywhere between 10-40A but only one 63A boat at a time due to the size of the things

They have on them washing machines, cookers, TVs, sat broadband, gaming consoles, fridges, freezers, electric heating etc.

 

[apprentice87]

No matter what they got on them i cannot see them drawing 63A on three phases.. That would be nearly 25kW.. Be same as a house drawing 108A

What size are the fuses in the cutout you got there and what is the supply impedance...

john..

 

[Dairyspark]

100A BS88s I believe, and I can't recal the supply impedance, I've got it written down at work

 

[apprentice87]

Ok, here is what i would do, I am not a qualified electrician though, so i would check with the others.

My approach though would be to do things so that others cannot pick holes in what you have done at a later date.....

Ok, so you have got 100A fuses. Check the supply impedance next, and supply voltage too. You will most likely find that the supply voltage is quite a bit above the nominal 400V

Now, next i would then calculate what the current would be, that i could draw from the supply, that would just drag the supply voltage down to 400V

Having done this, i would use whichever was the lowest, the calculated figure or the 100A as my "supply capacity"

I would size the cable to the DB so that at max supply loading i had a volt drop of about 1.5% and then i could allow another 1.5% to be lost in the cables to the sockets.

This way at least, anyone can plug in what they like, there will be no volt drop problems, and, as you will have the full supply capacity available at the DB, nobody can blame you if things do not go to plan.

For all you know people might start running welding sets and alsorts once you have installed all these nice sockets for them, and, it is reasonable i think, for someone to expect to be able to draw 63A from a 63A socket without the voltage dropping too low. As i say, make the thing future proof, cables are not that expensive...

All them 4 pole RCD's are not going to be cheap though!!

john

 

[NozSpark]

I think that this could easily come under the "Marinas and other similar locations" section of the regs TBH which will require individual RCD protection for each socket outlet

As for max demand.... If you are only ever going to supply 2 boats from this DB then I'd size for the 2 largest sockets

 

[Dairyspark]

I have selected a 25mm 4 core swa which at 100A gives a volt drop of about 1.9% and the volt drop to the sockets will be next to nothing, they are a meter at most away from the board, once it's done I'll take a photo haha it's Friday's job, and yes I'm going to assume since these boats have 63A inlets they can draw said power.

It's not covered under marinas as the boats aren't afloat in water, they are high and dry, if I'm being really particular (no doubt I'll get shot down) section 709 covers supplying power to pleasure craft and house boats in a marina or similar location (a place with fixed wharves, jetties, pontoons and piers)

Anyone on Facebook look up A.Noble and sons youll see what I mean lol

 

[Essex1]

It may be worth considering fusing down between the main head and your DB. You don't want an overload to blow the main each time.

 

[Doc Hudson]

230v Sockets

1 x 63A

1 x 32A

2 x 16A

400v sockets

1 x 16A 4 pin

1 x 16A 5 Pin

1 x 32A 4 pin

1 x 32A 5 pin

1 x 63A 5 pin

2 boats at a time and by varied means I meant some have 230v inlets som have 3ph 4 pin etc. So a selection of different outlets is needed

So you have up to two boats connected at a time but they could be either, Two 230v, or Two 400v, or One 230v and One 400v. By definition from the sockets you are fitting if you have two boats with 230v or two boats with 400v supply, then the max your sockets can provide is 63A + 32A (95A). If you have one 230v and one 400v what is the probability that they will both want 63A connections?  You don't say how long these boats are in the yard for and drawing power. Is it days, weeks, months and how many hours per day would they actually be drawing any significant power. I would have thought you could decide what max supply you are willing to give, not what they may want to take. In principal this is similar to a caravan park with 16A 230v connection provided, but typically limited to 10A or 6A per unit. Why not stipulate that the 63A connections will be limited to say 50A or 40A or even 32A max.  

Doc H.

 

[Essex1]

That makes sense. You could fit local OCPD to limit what can be drawn. Put up labels that say '32 amps max'.

Will these sockets also be used for maintenance equipment?

 

[Doc Hudson]

With no fixed loads and so many unknown quantities, type of connection, actual power needed, duration of load, number of boats, I cannot see any other reasonable way to do it.  If money is no object just engineer it up to the max on everything. But in the real world where budgets generally are involved decide what is a reasonable supply level and cater for that. What you need to look at is some past history of what loads have been supplied over the past 6 or 12 months. and what projected loads you have coming in for known work already contracted. Other than that it is pure guess work.

Doc H.

 

[ProDave]

Well if they don't count as "boats" when they are out of the water, then they must be "mobile or transportable units" instead then?

So that's still demanding rcd protection, no pme earthing.

 

[apprentice87]

Hi SparkyBob,

You say;

"I have selected a 25mm 4 core swa which at 100A gives a volt drop of about 1.9% and the volt drop to the sockets will be next to nothing, they are a meter at most away from the board, once it's done I'll take a photo haha it's Friday's job, and yes I'm going to assume since these boats have 63A inlets they can draw said power."

Having seen the photographs, i agree with you 1000%

If you installed 63A sockets, but with only, say, 32A available, even if you do it for the best reasons in the world, you can be sure that the first time someone actually wants 63A, that they will not be interested one little bit in your technical reasons as for why they have only got 32A, rather, they will just go around complaining that your installation is a load of crap....

As i say, having seen the photos, I think that once these sockets are installed, there is more chance of flying to the moon than of people NOT connecting up large welders, compressors, and plasma cutters....

25mm it is then!!!!

john...