“I'd rather regret the things that I have done than the things that I have not.”
― Lucille Ball

Tuesday, March 15, 2016

Repairing our electrical compound connection

This part of the wires were the cause of the problem,
I used my car to pull out the wires from the conduit
Sometimes in your life you make a big mistake, as I did five years ago.

Being an electronics engineer (NOT electrical engineer), I miscalculated what could go wrong if you put a set of electrical wires in a too narrow conduit pipe. This kind of subjects is never taught to electronics engineers.

I used a 3/4" PVC conduit pipe for two AWG #6 wires, which were rated for use until 60 degrees Celsius. The ampacity was about 60 amperes. The pipe was put in the concrete of the fence, running from the point where a split was made for a 100 amperes connection to the house and a 60 amperes connection to my workshop and garage, we call it bodega.

The only reason for using a 3/4" pipe was, that it would be cheaper than a 1" pipe. Well that turned out not to be the case many years later.

I didn't realize that the environmental temperature here at daytime is usually between 30-40 degrees Celsius, and that concrete is a kind of solar heat collector. The temperature can easily increase to even higher values, perhaps 50-60 degrees, although I didn't measure it. So even if you are using a moderate current, the temperature limit is easily met.

Just a few days before I would depart for a trip to Europe, July 2015, I noticed while working in my office that something was wrong with the electric connection, as the UPS for my communication equipment was clicking on, off, on, off, etc..

When I looked out of the window, I saw smoke coming out of a junction box on the fence. So I immediately switched off the main circuit-breaker at the electricity supplier's side and the circuit breakers at both ends of the split and started to investigate what went on. There was a shortcut somewhere in one or more of the legs of the tee split. So I removed the split connection in the junction box and measured the three circuits for a short circuit.

It turned out that the wires running from the split in the junction box to the bodega had a shortcut of ca. 60 ohms. The other two circuits of the tee were okay. This meant that there was a short-cut current of about 4 amperes, not enough to activate the main circuit-breaker of 120 amperes, but enough to start a smoky fire in the pipe and hence the smoke escaped via the junction box. So I could again join the wires coming from the supplier with the ones to our house, the house was saved again, but for the bodega I had to make a temporary circumvention.
The red wires on top of the fence served as the circumvention for six months

The problem was that the pump for our water supply was located in the pump-house in the bodega, as well as the pump for the swimming pool.

I decided to make a makeshift connection from the bodega to an outdoor outlet in the house for an air-con unit, which was not used. By doing this I had a connection with its own circuit-breaker. I used AWG #12 wires, sufficient for the drinking-water pump, but not for an additional swimming-pool pump.

After returning from Europe I had to find a solution to solve the problem and improve the design. There were two options:
  1. replacing the wires in the fence by new wires in new and larger conduit pipes, not in the fence, but on top of, or
  2. replacing the wires by aerial wires, using two or more poles, to bridge a distance of ca. 40 meters.
It took me months to finalize the design and to make the necessary decisions and to make a budget estimate. Especially option 2 was a difficult one as I didn't have experience regarding the distance you can bridge, depending on the type of wire to use (AWG # and material type: copper or aluminum). What I noticed recently was that DECORP, our electricity supplier uses #6 aluminum wires for drop-down wires from their low-voltage (220 Volt) grid to an individual customer.

Aluminum wire is of course much lighter than copper wire and can bridge a larger distance than copper, however I couldn't find initially a supplier for aluminum wire. I even went to DECORP, but they didn't want to sell to me.

So finally I decided to go for option 1, using 1" conduit pipes and AWG #6 copper wires which can resist temperatures up to 90 degrees Celsius and able to resist wet conditions, type THHN/THWN. The conduit pipes are just 1" schedule 20 GI pipes used for water supply, as I wanted to have a more robust implementation because of the construction with fence posts every 9 meters supporting the pipe.
Here is a breakdown of the cable lettering to help make some sense of the wire specification.
  1. The "T" stands for thermoplastic insulated cable.
  2. A single "H" means the wire is heat resistant.
  3. "HH" means that the wire is heat resistant and can withstand a higher temperature. This wire can withstand heat up to 90 degrees Celsius.
  4. A "W" means that the wire is approved for damp and wet locations. This wire is also suitable for dry locations. If used in a wet environment the heat resistance drops to 75 degrees Celsius.
  5. The "N" means the cable is covered with a Nylon skin as extra protection.

Note: after the decision I made for option 1 and the cable type, I found a supplier, which is GPDX on Burgos street in Dagupan.

I added a separate circuit breaker box to the tee split, such that now I can switch off the connection to the bodega and lowered the breaker limit at both ends to 50 amperes.

I will also replaces all the wires in the fence used for the lights and some outlets, but that is my next project.

See the pictures below for an overview of the steps in this project.

black junction box after the fire

connection to the bodega is disconnected, the house is reconnected

air-compressor was used to get rid of the smokey dirt in the junction box

a new junction box is installed to connect the new to the old wires near to the bodega

installation of new conduit pipes and wires is done from end to to start

wire specs: AWG #8, high temperature up-to 90 degrees Celsius, dry and wet usage

ampacity table

threads of GI pipes are usually of bad quality and need refurbishing before using

pipe stock left for this and another project,
black is schedule 20, red schedule 40

installation is done from end to start,
red wire is the circumvention

almost done, only ...

... cut the last pipe at suitable length

install a new circuit breaker box for the bodega

project finished, red wires removed


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