Volt Drop Charts

[Garry Blackburn]

Does anyone know of a chart which would convert volt drop in AWG sizes to Metric sizes as used here in the UK. I've found numerous charts on US websites for AWG, but none for metric.

Thanks

Garry

[sitelights]

A pocket digital voltmeter (of known/tested accuracy) that reads to 2 decimal places (1/100th of a volt) would allow you to determine voltage drop under actual field conditions. We routinely measure and record the voltage at the 120v source (usual range 115-125v) and then measure and record the secondary voltage of the system with all lamps operating: at the transformer and at the first, middle and last luminaire of each cable run. Try this on some of your previously installed systems.

After collecting actual readings for a few systems you will find that you can accurately forecast the voltage at each lamp in the same way an experienced photographer can anticipate camera settings without metering. Understand that we use 10 gauge cable, 20w lamps and transformers with 12v, 13v, 14v secondaries and adjust the output voltage to achieve a min/max of 10.5v to 12v throughout the system.

Our configuration of choice is the "loop" where both the cable ends are connected to the transformer being careful to maintain polarity. By limiting the load to 200w or less on a 300w transformer we have found that 250' to 300' of cable can be used with this method. This is well beyond the theoretical limits shown on voltage drop tables.

Confidence is a function of experience. I buy the installers' lunch if my design fails to
meet our voltage standard.

By the way, I understand that mains wiring in the UK uses a "ring" (loop) configuration.
Is this true?

[landscape liter]

I agree with your sentiments up until you stated that you believe in using the loop method. Have you considered the potential hazardous result if the homeowner or another installer serviced or went to add more lights on to your system and they failed to maintain polarity ?

[Garry Blackburn]

I do regularly test voltages on installations, but we don't have the luxury of multi- tap transformers over here (yet). We have a fixed secondry voltage of between 11.5 and 12.5 volts but I will be discussing this with my supplier.
Yes we do use a loop system (ring main) for our socket outlets in the UK, but there's talk of replacing this in the future with a radial "branch" circuit. The reason for this is that the ring main is 2.5mm2 24amp cable which starts and finishes at the consumer unit and is protected by a 32a circuit breaker. Theoretically, should an open circuit situation arise the circuit breaker would not protect the cable. So the idea is that we install radial "Branch" circuits protected by a 20a circuit breaker, where you can add extra sockets without the worry of maintaining the ring.

Garry

[Garry Blackburn]

When using 20watt lamps, in fixtures rated at up to 50 watt, do you use transformers with sufficient capacity to take 50 watt, or do you supply the client with a specification (including lamp wattages) on completion of the installation. I do the latter, but it concerns me that the client might up the wattages and overload the transformers, thus creating a potential dispute.

Garry

[landscape liter]

Unfortunately There is nothing you can do about tampering with your system once you are gone. From your previous messages I understand that your transformers in the UK are not equipped with breakers or fuses on the secondary side of the transformers. To limit your liability from shorts or overloads you can install a 15 amp slow blow in line fuse close to your transformer for all 12 gauge cable runs . A 20 amp for all 10 gauge runs. These fuses are the same ones used in automobiles and should be readily available even in the UK I would imagine. To head off any potential dispute. Record amperage readings on every cable run and clearly number and mark with endelible ink somewhere inside the transformer case for future reference This way there will be no contention when your original reading was 7 amps and it somehow became 17amps after fixtures were re-lamped.

[sitelights]

There is something that can be done about tampering and we've been doing it for 15 years. All of our installations include 3 full years of maintenance including lamps. Our
final invoice states: "The standard 3 year warranty on all materials (including halogen lamps) and workmanship applies to this installation." A statement to this effect also appears on our web site. Our final invoices also provide the client with an accurate cost
of operation based on lamp load x hours of operation x local power company rate.

We work for high-end clients and do not put the burden of maintenance on them. After the expiration of the original warranty we offer a service agreement for an additional 3 year period that duplicates the original warranty. Since the client has been insulated from maintenance costs during the warranty period we supply a brief history of maintenance and the attendant costs if they had been billed. We also state our service costs for typical maintenance if they would prefer to be billed on a per-call basis. This allows the client to make an informed decision. About 75% of our clients opt for the service agreement by sending us a check for the amount stated on the pro-forma invoice included with the service agreement proposal. If a check is not received within 90 days we send a follow-up letter providing specifications and other information regarding the safe maintenance of their system. Many of our systems have been serviced exclusively by us since the mid '80s.

This post should actually be under the Warranty heading. Questions or comments about the implications of this post should be posted there.

[landscape liter]

Maybe in a perfect world but this will not in all cases prevent tampering. Some people by nature like to tinker with things they aren't qualified to tinker with even when a solid warranty is provided with written info or not. It is also a fact that people are lazy and sometimes will have the person who is most convenient at the time (ie: handyman, gardener) change a lamp instead of picking up the phone to call the original installer or do it themselves. I have heard excuses from customers when i've questioned them go something like this; "Well, we didn't want to bother you for only a few lamp burnouts". meanwhile it's no bother and it's why we are in business. There is no way to effectively mitigate the motivation of some people.