Wiring in a 240v backup generator in a SWER area

March 6, 2011 by GOIloilo | 40 Comments

Wiring in a 240v backup generator in a SWER area. This is information which will only be of interest to a few. It’s about installing a 240v generator having two load or “hot” terminals in the rural Philippines served by utilities using the single wire earth return system (SWER) which has only one 240v load wire.

The wiring in our Philippine house is described at http://myphilippinelife.com/our-philippine-house-project-philippine-electrical-wiring/

Single wire earth return (SWER) or “is a single-wire transmission line for supplying single-phase electrical power from an electrical grid to remote areas at low cost. Its distinguishing feature is that the earth (or sometimes a body of water) is used as the return path for the current, to avoid the need for a second wire (or neutral wire) to act as a return path. It is principally used for rural electrification.”

Our electric utility is a cooperative, Ileco 1. Ileco supplies 240v residential service with two service wires, a 240v load and a neutral or ground. We wired our house accordingly, using single-pole breakers. We always anticipated that we’d have a backup generator and so we installed underground two #10 AWG wires from the panel box to the storage room in the garage, where we proposed to put the generator once we bought one.

On the face of it, shopping for a generator seemed pretty simple. Almost all of the Philippines uses 240v wiring so we just buy a 240v generator and hook it up to the two leads to the panel box and voila we have our backup power. It turned out to not be so simple. We have had very good luck with our equipment purchases at New OK Marketing on Ledesma Street in Iloilo City, across from the Robinson’s mall. In our experience, they stand behind their products. We bought a cement mixer from them which required repair. The same day they sent a man, a truck, tools and parts to our property 22KM from New OK and replaced the mixer main bearing. They did it promptly, without argument. Knowing that a generator will require parts and maintenance over the years, we wanted to buy from New OK and we did.

While New OK sells several brands of generators, the owner recommended the Chinese Weima generators as cheap and reliable, with good availability and fair pricing of parts. We were toying with buying a Honda generator but the owner told us not to waste our money. The basic Honda generator we had in mind sells for about P37,000. We ended up buying a Weima 3200 generator for P13,000. The generator is rated at 2800 watts. Since we only wanted to run lights, fans and refrigerator, we calculated our load at 1,500 watts. Since motors can draw much more current when they start up, we felt that the Weima 3200 would work for us. We wanted to get a unit light enough for us to put in the back of our Toyota Innova to take it in for service. The Weima 3200 weighs about 45 kilos or just about 100 lbs. Moving to a generator in the 5,000 watt range, or getting a diesel generator would mean a 200 lb. unit, too heavy for us to load.

Weima 3200 Gasoline Generator

We have had good luck with New OK Marketing

With excitement, we got our new generator home. We started it up just to hear it run. It started on the first pull. Then Bob got out his voltmeter to check the output of the three terminal plug on the front of of the generator. There was a three prong twist-lock outlet. The outlet has three terminals, one load, one neutral and one ground. There was also a separate terminal to ground the generator frame. The voltmeter showed that neither of the output pins provided anything like 240v. One load pin measured 164v to ground and the other about 56v to ground for a total of 220v. The generator was obviously set up to be installed at a residence with TWO load leads. The two generator outputs would then feed about 220v to the panel box. So, how was it possible to use the output of the generator when our system has only one load bus. Bob was kicking himself (as he should) for not anticipating this problem.

Since we did not anticipate the problem, we did not shop accordingly. Possibly there are generators which produce 220-240v to a single load terminal, but the fact is that just about all urban areas in the Philippines (including Iloilo City) use a two load wire system and most generators are going to be purchased for use in urban areas, so that’s the generator configuration that is likely to readily available.

A reader of the myphilippinelife.com blog, Andrew Archibald, came to our rescue. All backup generators must be connected in such a way that voltage from the generator can never feed back into the utility lines. To do so would be a grave danger to utility workers. Generally a DPDT transfer switch is installed which allows either the generator or utility power to flow to the main panel box. When the switch is set to “generator” all connections to the utility grid are cut off.

100amp DPDT Switch

Regarding the above illustration, the top two wires are the feed from the utility company, the bottom two wires are from the generator and the middle pair feed the load and neutral buses of the panel box. There is a cover which encloses the switch but it’s removed so that the wiring can be seen.

With the transfer switch in the normal “utility” mode, the panel box is powered by one 240v load wire and one neutral, both from our electric utility company. The house wiring mirrors this. Each outlet is powered by one 240v load wire and one neutral. Mr. Archibald’s solution is to essentially transform the house circuits when the transfer switch is set to “generator”. Instead of the one “hot” load wire and one neutral from Ileco, the house wiring is supplied by the load and neutral wires from the generator, which, taken together, equal 220v delivered to the outlets. In essence, the wiring of the transfer switch changes the house wiring from the SWER system to a more conventional urban two load wire system. This is the basic solution, but to apply it safely required thinking through some complex neutral and grounding issues. We could never have done this on our own. Mr. Archibald determinedly thought through the issues through and proposed how the wiring should be done. Below is a wiring diagram which shows some aspects of how the transfer switch and panel box were wired. This is only to show how we solved our problem, but it could be very unsafe to try to apply the same solution elsewhere without advice from a good electrical engineer. Note that with the generator in operation, the neutral is delivering some of the load.

Wiring diagram for generator hookup

We rewired our transfer switch, panel box and generator following Mr. Archibald’s suggestions. It worked almost perfectly. The very next day we had a 8.5 hour power outage and ran the generator for 6.5 hours. It mostly powered the washing machine, water pump and refrigerator. All of those ran fine.

The Weima generator ran flawlessly, using approximately five liters of gasoline for the 6.5 hours or about .75 liter per hour. The fuel tank holds fifteen liters, so overnight operation without a refill seems realistic.

Normally we would not use the generator during the day. Our two main reasons for having a generator are for very long outages, such as in the wake of a typhoon, when we’d need power for our large refrigerator, and being able to run our outdoor security lights at night. We live in a somewhat isolated rural location and feel more vulnerable when our property and the entire neighborhood is pitch black. However these long outages have a silver lining; the karaoke machines and boom boxes all fall silent!

We’ll keep researching generator availability and wiring options and will post any new information we find. Likewise, we’d appreciate any comments or suggestions from readers.

My Philippine Life

Personal perspectives on retirement life in the Philippines

Wiring in a 240v backup generator in a SWER area

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