Frayed service cable / power quality

Frayed service cable / power quality

 

What type of electric service cable damage are you looking out for?

If you can see exposed aluminum strands on your service entrance cable, it has frayed to the point where you should replace it. Cost may vary from $750 – $2200, depending on your service capacity (usually between 100A – 200A for residential electric accounts) and the capacity of your replacement service (for those wanting central air conditioning, an upgrade from 100A to 150A or 200A will often be needed; subsequent solar PV or micro wind power installations over 5kW capacity may be cheaper to install if the existing service is larger than 100A).

Typically, sunlight and weather work in tandem to disintegrate the outer casings of cables more than 30 years old. Once exposed to water and weather, the braided ‘neutral’ conductor becomes subject to corrosion. Though it is aluminum (typically water-proof in isolation), proximity to lime in the runoff from masonry surfaces, and other causes may result in the complete failure of the thin, exposed strands of aluminum as as a current-carrying conductor. The result is that the building grounding system (assuming it is present and complete) will take up the slack of current that should be flowing back to the utility lines. If the grounding system is in any way deficient, dangerous voltage and/or current may develop on grounded objects in the house, including any pipes (water, drain, gas, radiator) and sometimes metal ductwork that has come into contact with pipes or that has been bonded intentionally to an electrical outlet’s equipment grounding conductor. Single pole voltages in the building (120V circuits) may operate at fluctuating voltages, and multi-wire branch circuits may impose intermittent voltage double the normal, at 240V, as the ‘neutral’ connection with the utility service wires comes and goes intermittently due to progressive corrosion of a frayed service cable.

Background: What’s a service entrance cable?

Most service entrances in Philadelphia are overhead using type SEU cable, which is rated for both underground and exterior sunlight-exposed installations, where not subject to physical damage (such as from a car bumping against it, if installed on a wall adjacent to a driveway).

SEU cable consists of weather and sunlight-rated insulated ungrounded conductors (‘hots’) inside a braided wrap of grounded (‘neutral’) conductor. Where used as service entrance cable, the system ‘ground’ and the ‘grounded conductor (‘neutral’) are one and the same. Everywhere beyond the building service disconnect, the grounding system and grounded conductor (‘neutral’) must be kept isolated from each other. Protecting the insulated ‘hots’ and braided ‘neutral’ is an outer layering of fiber tape and water-proof plastic casing (older cables may have been composed of a tar-impregnated fiber casing).

 

See also:

• What is a service disconnect?