What circuit type is this?

[RF Lighting]

Just doing some VD calculations for a circuit I have to install.

It is a new submains in a community center which will eventually supply a stage lighting dimmer.

Now for the purposes of maximum % permissible VD, would you class this circuit as a lighting or power installation?

 

[securespark]

Is the submain purely intended to supply lighting only?

If there is a possibility it may be used for power, design it as such.

 

[oharaf]

Hi Rob, I would go with Secure on this one, you know what people are like, its for this when ordered then quickly they bolt all sorts on!!!

The Community CENTER where in the U Sof A is it?

Sorry!! I just can't quiet break the old teachers mould yet, still my Effing & Jeffing has improved immensly (whoops!!!!)

 

[ban-all-sheds]

Sorry!! I just can't quiet break the old teachers mould yet

We'll noisy break it then.

PS - the incorrect ' in "we'll" was intentional

 

[Spark123]

Just doing some VD calculations for a circuit I have to install.

It is a new submains in a community center which will eventually supply a stage lighting dimmer.

Now for the purposes of maximum % permissible VD, would you class this circuit as a lighting or power installation?

As it is intended for lighting go for 3% max VD, then it wont matter.

 

[captaincargo]

Id go worse case ,just in case

 

[Adam_151]

Very black and white, this, but sometimes it can help to look at this way

The submain itself will comply if the voltage drop between the origin and the subboard is less than 5%, you, of course, need to allow for the final circuits from this subboard to drop some (and where there are lighting circuits, this of course needs to be a max of 3% between point of use and origin)

As you have stated you will be running lighting circuits from that subboard, you'll have to work on 3% for both submain and final lighting circuit, I seem to remember there being a rule of thumb to drop 2/3 of the allowed in the submain and the final 1/3 in the final circuit, so by that school of thought if the submain is sized for 2% volt drop (or just under) you should be about right?

 

[Pensdown]

It really depends where the dis board is in relation to the origin and the furthest point of any final sub circuit.

If the dis board is say 100mtrs from the origin and the longest FSC is 10mtrs then you can drop most of the voltage in the sub-main.

But if the dis board is 50mtrs from the origin and the longest FSC is 60mtrs then you would need to drop most of the voltage in the FSC.

IMO it's often easier and more cost effective to reduce the volt drop in the sub-main and leave yourself more to play with in the sub-circuits. As a general rule I use a maximum of 2% for sub-mains.

 

[ericmark]

There are two rules you can use.
1) 3% volt drop for lighting.
2) Follow manufactures recommendation.
So if the light dimming unit says it can be supplied with 200 to 300 volt you can allow a volt drop a lot more than 3%.
Sometimes we have to use common sense rather than the rule book. We realise the reason we have the 3% rule is so discharge lighting will not fail.
Since it is supplying a dimmer unit this is hardly an issue but what else will it supply

 

[maltaron]

I note this job is to supply stage lighting. This is vastly different from normal lighting. Just a very simple rig of 6 x 1 k theatre lanterns is nearly 30 amps and diversity may not apply as they are likely to be all on. You say that this MAY be used for stage lighting, if that means that staging companies will be brought in on certain occasions to supply the stage lighting they are likely to expect a minimum 3 phase 32amp supply.

 

[Spark123]

You can ditch diversity to a certain degree. If going 3 phase route then you can use the 3 phase calculations howver you'd need to take advice on harmonic currents from dimmer packs adding up in the neutral.
I only have 7x 60A (42x10A max channels) dimmers on my setup, the whole stage when clamped only draws about 35A per phase

So if the light dimming unit says it can be supplied with 200 to 300 volt you can allow a volt drop a lot more than 3%.
Sometimes we have to use common sense rather than the rule book. We realise the reason we have the 3% rule is so discharge lighting will not fail.

I sort of follow what you are saying however to get the lamps output their maximum lumens you need to have knocking on the correct voltage.
Even though the final circuit likely ends at the socket for the dimmer you also need to remember there may be a great big lump of HO7RNF stuck on the end of it up to the fixture too.

 

[RF Lighting]

The new submains is a dedicated supply for a 48kW stage lighting dimmer.

I'm designing the circuit for FLC with no allowance for diversity.

It's a TP&N supply about 40 meters from the origin. The longest outgoing circuit is about 15 meters (10A circuit wired in 2.5mm²)

 

[Spark123]

48kW equates to about 70A per phase, however volt drop will probably be more a deciding factor.
Taking into account the extension lead if fully loaded to 10A (which hopefully it wont) will have a 1.2% volt drop, if you are aiming for a 3% volt drop then you can have a 1.8% volt drop in your final circuit.
In 3 phase leccy this equates to 7.2v.
You have a 40m run with 70A per phase, so the maximum mV/A/m is given re-arranging the formula:
7.2= (mV x 70 x 40)/1000
7200 = mV x 70 x 40
7200 / 2800 = 2.57 mV/A/m maximum
From the VD charts a 25mm 70ºC SWA configured as 3 phase has a resistive VD of 1.5mV/A/m so assuming it meets all the other criteria then it should do - need to check the neutral current thing.
Oddly enough, my lighting rig is fed from a 63A supply via a 25mm 4C SWA too, only about 20m long tho.

 

[sparkyspike]

its for this

I just can't quiet break the old teachers mould yet

old teachers

I hope you weren't an English teacher...

 

[Spark123]

Think ohraf is meaning you can never tell what someone else will want to bolt onto the circuit afterwards so it is always a good idea to leave a bit of capacity and design for the most onerous conditions.
As for the teachers bit, think he is jesting at RFs spelling of Centre being the American one.