Power to a trailer?

[RyanM]

Problem:

We have a refrigerated trailer which needs power to it to keep it cold when it isn't hooked up to a cab.

The trailer is approx 25m away from the building, and stays there all week. Until a Friday when an empty tailer comes and the full one taken away!

The 'easiest' option is a long extension protected with a RCD. But I cannot see this being the right way to do it!! Where the trailer is parked, it is a working yard so protection to the cable is key! Also protection to the user when the connect/disconnect the plug.

From Section 717 I can see that a TN-C-S system cannot be used, as it won't be monitored all the time, or used by a skilled person. What would be the best system to use?

Any obvious ideas other than burying or suspending the cable?

Or will it be ok running an extension to the tailers if it has correct protection?


Thanks a lot

 

[RyanM]

Also, Section 717.52.1 says a flexible cable is permitted to connect to the unit.

How long can this flexible cable be? I.e. 25m ok?

 

[bongos]

How long can this flexible cable be? I.e. 25m ok?

This will depend on volt drop and your desired load.

Also EFLI will need considering. But if you are switching refrigerators on/off then you will have a higher inrush current, meaning a C type (or possibly D type) MCB will be more appropriate. For this you would require lower EFLI readings.

If the unit is going to be there permanently then I would think using a flexible cable is probably not the best idea. Especially as you would want the unit on it's own circuit. Also I think you would want to design the circuit as to avoid the use of an RCD as nuisance tripping could lead to the loss of the fridge contents.

What load are the refrigerators?

 

[ban-all-sheds]

Also protection to the user when the connect/disconnect the plug.

What hazards do you think someone might face?

From Section 717 I can see that a TN-C-S system cannot be used, as it won't be monitored all the time, or used by a skilled person. What would be the best system to use?

That's talking about an electrical installation within a mobile unit.

Are you sure you're competent to be doing this work?

Any obvious ideas other than burying or suspending the cable?

Some kind of cable protector ramp? What sort of traffic will be going over it?

Or will it be ok running an extension to the tailers if it has correct protection?

Yes.

How long can this flexible cable be? I.e. 25m ok?

Don't see why not - just do your usual loading, volt-drop & R1+R2 calculations to get the right size.

 

[RyanM]

I will get the exact size of the refrigerated unti this afternoon when it stops raining!

We have loads of 4mm SY cable which I would probably use, so for the distance the VD will be ok. Although I haven't worked it out yet (which I will).

It isn't permanent as such, as it's a stop gap until we get a bigger cold store, but we might use the trailers for a year or so......

bongos, good point about the nuisance tripping, and then lack of refrigeration! In what other sense could I design the circuit to allow it do be safe, as I would need to use a RCD. Or do you mean using something other than a flexible cable? I.e SWA burried?

ban-all-sheds, apologise for my lack of knowledge. I am just starting out and am learning everyday. Which is why I asked for some advice on here, rather than just going ahead and doing something I'm not too sure about.
Hazard wise, I was thinking of the user disconnecting the plug/socket under load and in the rain for example.
Good idea about the ramp protector! The main thing is we have a fork lift (small one), pallet trucks etc. But also I thought if the trailer was removed, then a new one brought, the driver could go over the cable and damage it.


Thanks a lot for the help up to now!

 

[ColJack]

we need a picture of exactly where this trailer is parked..
you may need to install a hook up point similar to a caravan park..
a large steel post with a waterproof plug / isolator on / in it..

or park the trailer closer to the factory

 

[bongos]

It isn't permanent as such, as it's a stop gap until we get a bigger cold store, but we might use the trailers for a year or so......

I'm sure someone on here recently said "there isn't anything as permanent as a temporary installation..."

In what other sense could I design the circuit to allow it do be safe, as I would need to use a RCD. Or do you mean using something other than a flexible cable? I.e SWA burried?

Have a look at 411.3.3 for how/if you can satisfy the requirements to avoid using a RCD.

Hazard wise, I was thinking of the user disconnecting the plug/socket under load and in the rain for example.

Could be a problem in Stirlingshire...

 

[Spark123]

From Section 717 I can see that a TN-C-S system cannot be used, as it won't be monitored all the time, or used by a skilled person. What would be the best system to use?

That's talking about an electrical installation within a mobile unit.

I think there is a specific reg re the supply to the trailer not being TN-CS unless certain criteria are met.
O/P, what type of supply do you have? TN-CS, TN-S or TT?
If you have TN-CS then the only real way forwards is to make that particular circuit into a TT and not use the PME earthing system.
I'm thinking something along the lines of SWA to a blue commando type socket and a short flex to the trailer. How open to the elements is it? The blue commando sockets I am thinking of come in IP44 and an IP65 flavours, you see them on camp sites all the time.

 

[ban-all-sheds]

Those regulations apply to mobile units such as OB trucks, workshops, offices, catering facilities etc, i.e. things which have electrical installations (CUs, circuits, accessories), not to a large portable appliance.....

 

[RyanM]

Here is a rough pic of the trailer location. Unfortuntaley it cannot go near the building due to it needed to be loaded up.
We did think about a metal post bolted to the floor, but from other damaged we've had from the fork-lift/wagons we didn't think it would last long!




I had a read through section 411.3.3, but think I do need to use a RCD. Which might mean nuisance trips

The socket will be open to the elements fully. The plug on the trailer is slightly undercover, but not really. Also I will be needing to use a red 32A 5 Pin Socket to match the plug on the trailers.

I will double check what Earthing System is in place, I'm 99% sure it's TN-C. We have our own sub-station on site.

 

[RyanM]

Just double checked, and out Earthing System is TN-C-S, which means I cannot use it as it won't be under supervision.

But, what does (ii) of 717.411.4 mean when it says:
the suitability and effectiveness of the means of earthing has been confirmed before connection is made.

How do you confim the earthing? Bearing in mind every time it is unplugged and plugged back in, it will probably be by a lorry driver?


Thanks


EDIT: OR, as Ban-all-sheds says, the trailer doesn't apply to this?

 

[ColJack]

no way you can park it closer to the compactor? you could run the cable alongside that then..

another option would be something similar to what they have at airports for the planes.. a hook up in the ground.. but then you're talking silly money..

what kind of traffic do you get round the sides of the units?

is there not a fence you can park near and run the cables next to that?

try a drive round some of the large supermarkets and see if you can see what their set up in in the loading bays.. they often have extra fridge trucks around x-mas times.

is your yard concrete?

hire a road saw and cut a 2 inch channel in it to the middle of the trucks, then get a 2 inch u shape covers made to stand over the cable.. ( or a 4 inch channel, fit a duct then concrete it back in.. )

 

[ColJack]

View media item 20978
you could put in a lamp post and put the hook up next to it.. there's really no excuse to smack the forklifts into it then..

if you tell us where the factory is we can google earth it to get the layout..

 

[Steve]

Lorry drivers will ALWAYS hit obstacles in their way. Put a post there and it WILL get damaged. One lorry driver reversed into our roof overhang at work once. Theres a couple of lamp posts at another shop that are at a 10 degree angle, and a concrete bollard whose top is missing, its just a stump.

No way the trailers can be parked next to the building - parallel with?

One thing I thought of - ColJack's idea of a channel to the trailers, but at the trailers, dig out a manhole about a foot deep and fit a socket in there. You'd need some form of drainage and cable access though.

 

[Spark123]

Those regulations apply to mobile units such as OB trucks, workshops, offices, catering facilities etc, i.e. things which have electrical installations (CUs, circuits, accessories), not to a large portable appliance.....

There has got to be something attached to the vehicle even if it is just a refrigeration unit. I personally don't like the concept of attaching TN-CS to the exposed metalwork on a big lump of metal which is being lugged around the country from time to time.