Ring vs Radial for minimum voltage fluctuations

[antigua finedining]

I'm building a new property consisting of 4 sperate discrete buildings, all roughly in a straight line. My question: Is there any advantage to connecting the buildings supply in a ring rather than just daisy-chaining them (i.e. radial)?

I was planning to run a single 1 AWG backbone supply up the middle of the property and spur off each building (radial). However I'm concerned about the last building seeing voltage fluctuations when the first building has high current loads... So instead if I run 2 x 4 AWG in a ring configuration would this benefit from reduced voltage fluctuations at the extremities?

 

[pc1966]

You can run some calculations to see the effects for any combination with a bit of time and a spread sheet! But you also should factor in the supply impedance as you will always have that as a common factor no matter what layout you consider.

You need to be careful if the total load is more than the #4 AWG cable can handle that is will be reasonably distributed around the buildings neither 'leg' gets too much current.

Using 4 separate sub-mains to each building would solve the between-building effects, but not heavy loads in the same building impacting on the supply. Also more cable costs!

 

[pc1966]

What currents and distances are you looking at? The usual requirement in the UK is for no more than 5% voltage drop, or 3% for lights (but with LED that is a bit out of date). On longer cables that can become a bigger sizing factor than the current carrying capacity (ampicity).

 

[antigua finedining]

What currents and distances are you looking at? The usual requirement in the UK is for no more than 5% voltage drop, or 3% for lights (but with LED that is a bit out of date). On longer cables that can become a bigger sizing factor than the current carrying capacity (ampicity).

Many thanks. In total it will be 70 amps for all 4 buildings on 220v (with building "M" having the highest loads). The longest distance from supply to Bed 1 is around 400ft. I've been working on calcs to keep drop below 4%

 

[antigua finedining]

You can run some calculations to see the effects for any combination with a bit of time and a spread sheet! But you also should factor in the supply impedance as you will always have that as a common factor no matter what layout you consider.

You need to be careful if the total load is more than the #4 AWG cable can handle that is will be reasonably distributed around the buildings neither 'leg' gets too much current.

Using 4 separate sub-mains to each building would solve the between-building effects, but not heavy loads in the same building impacting on the supply. Also more cable costs!

I've run some calculations for various scenarios like you suggested...I just assumed that ring would be better and that's why I'm asking on the forum for confirmation... But having run a few scenarios I can't see the benefit at all (and in some scenarios radial gives smaller losses!)

So simple 1 AWG radial it is then (don't want to run 4 sub-mains since the cable cost will be massive)

 

[pc1966]

The ring has advantages for loads that are physically in some sort of a ring!

In the UK we have a "ring final circuit" that is only seen in countries that used fused plugs, so basically the UK and a few related countries. But that makes sense as you have a single 32A breaker feeding any number of sockets connected as a ring, with each socket able to deliver up to 13A (but with smaller fuses like 3A common for low power items). Here we slightly under-size the cable (2.5mm rated 20A) on the basis the loads are limited and distributed leading to less copper costs, and due to the double paths a more reliable/redundant earth. Typically a RFC is limited to 100m^2 area, or commonly one per-floor to limit the impact of a fault.

Where you also see a ring layout in the UK is for high voltage distribution in a city. But there the ring is normally left with a link point open (so two radials in use, typically lowering the max fault current) then the link points can be changed to close one and open another two leaving one segment of cable isolated, etc.