A recent circuit troubleshooting job at 44xx Locust St. probably started when a plug-in electric space heater overloaded a knob-and-tube circuit serving a dozen locations besides the one where the heater was connected. Space heaters typically consume 100% of permissible circuit load, although when connected to a knob-and-tube location, they may be sharing with a dozen or more lights and other receptacles.
The overload might have had no consequence if a wire-nutted splice in a basement ceiling junction had been better made-up. Unevenness in the wire twist combined with absence of any metal bonding sleeve inside an old ceramic wire-nut probably allowed oxidation to partially insulate the spliced wires from each other. When the heavy heater load subjected this poor connection to overload, the connection failed entirely — probably due to arcing and burning of the tiny contact-points that remained. A problem such as this could be identified before it manifested as a complete fault, by use of a loading receptacle tester to analyze voltage drop under a load of 12A or 15A (see FAQ-Voltage Drop by SureTest(TM)).
The primary cause of the difficulty was probably poor HVAC service to the room. The use of space heaters in a fully-occupied building should not be necessary (and probably will not save money) if the central heating system functions properly. Correcting this heating deficiency would be the best inoculation against similar future overloads from use of space heaters. However, summer air conditioning could still cause a similar overload. Installing a dedicated heater/AC circuit to each bedroom in the building would allow for heater use, if necessary, and for AC use that is likely. The new circuit’s grounding facility could be used to ground one or more existing non-grounded locations to provide for proper surge protection for computers and other sensitive electronics.
A distant third-place ‘solution’ could be to ensure that no more than one space heater or vacuum or hair dryer or other high-power appliance gets used on a knob-and-tube circuit at any given time, and to provide a space heater that has low- and medium-power controls rather than only one power setting (heaters with a single power setting usually will operate at 1440W or 1500W — the maximum allowed on a knob-and-tube circuit). It will be extremely difficult to properly manage use of knob-and-tube circuits where dedicated (or, at least, new) circuits have not been provided and indicated to occupants for use by high-power appliances.
Other issues identified during this 2.5 hour service call to troubleshoot circuit problems include:
- (4) Multi-wire branch circuit pairs lacked a handle-tie across the breaker pairs for safety to ensure all circuit components are turned off when any one part is manually shut off or automatically tripped due to overload.
- (1) Multi-wire branch circuit (included above) connected at breakers not adjacent to each other.
- (1) breaker has been ‘double-tapped’ in violation of National Electric Code. One circuit should be moved onto a new breaker.
- At least one pair, multi-wire branch circuits served by a 20A breakers where the wire capacity is only 15A (this problem may be addressed at the same time as the missing handle-tie noted in ‘Item 1′, above).
- Service disconnect equipment (breaker panel) lacks a supplementary grounding electrode. Building bonding jumpers across water meter and between metal piping systems may also be lacking.
- Numerous missing device covers (receptacles and switches). Some covers were removed during pest-control work and may be somewhere on site. Pest control contractor should replace or pay for replacement, unless another arrangement was made.
- Knob-and-tube circuit serving 2FL Rear serves all receptacles and lighting for bedroom, closet, entry area, and bathroom including lights and GFCI receptacle. Especially prior to admitting woman tenants (or anyone likely to use a hair-dryer), the bathroom receptacle should be re-fed by a new, dedicated circuit as required by NEC for new construction bathrooms. This bedroom (and all bedrooms in the building likely to house long-term occupants) should be provided with at least one dedicated circuit that would provide for window air conditioner use in summer and space heater use (if necessary due to central heating deficiency) in winter, without risk of overload to the already heavily-loaded knob-and-tube circuit.
See also:
- Costs for common and affordable residential electrical upgrades
- How to not burn down your house using plug-in electric space heaters
- Learning to live with old wiring in Philadelphia homes
- What is a grounded receptacle?
- SureTest(TM): Voltage Drop FAQ
Licensed Electrician Robert Monk Troubleshoot circuit problems in old Philadelphia home Copyright Robert Monk, 2012
