Troubleshooting by phone saves customer service call expense
I recently had a call from a concerned customer, about an electrical burning smell in the house, after demolishing their own kitchen in preparation for a renovation and remodel. Sweeping up afterward, they saw some slight sparking on old wires that had had a lighted doorbell button connected.
With a few more questions, I quickly steered her into the basement and toward the following theory:
- The bell wires had become crossed (shorted).
- Short-circuit current through the bell system transformer operated the transformer at high current for extended periods (whereas it is designed to operate through the resistance of the bell button lamp when at rest, or the bell motor/chime when the button is pressed — momentarily not continuously).
- The bell transformer windings (tiny copper insulated by a tiny layer of insulation to allow the windings to pack densely together for maximum effect / minimum size) burned through their insulators and/or opened the circuit by burning a winding conductor out like a lightbulb filament. This was the burning smell.
Subsequent inspection bore out the theory, and the customer has had the transformer disconnected from the circuit by a local handyman friend, rather than call for outside service.
Bell, intercom, and thermostat/control systems typically operate on low voltage AC circuits (under 48V), allowing the use of freer wiring methods, including smaller wires (16-22 guage), exposed wiring acceptable, and splices without junction boxes acceptable. Bare skin will not pass current (permit a shock) below 70V (women typically can’t be shocked below 85V and men below 90 or 100V), and building structure is similarly safer from low-voltage wiring than 120V household power wiring.
Transformers energize the bell/control systems using power from the household 120V power system. AC on the transformer input coil induces a ratio of AC voltage on the transformer output coil corresponding to the number of windings in the two coils. A typical winding ratio of 10/1 yields 12V AC from the 120V AC input.
Since the failure mode of transformers (usually due to a short circuit, or continuous rather than intermittent use) is to open the circuit, even short circuits on the low voltage side aren’t likely to present a fire or personnel safety issue. Typically, the transformer acts as its own circuit breaker.
Off-site Links ->
- Annapolis Home Inspection, LLC Aluminum branch circuits, homes 1965-1972
- ComplianceAndSafety.com OSHA Electrical Safety Training
- Electric Monk TV (YouTube) Video channel for PhillyLicensedElectrician.com Robert Monk
- EnergyConservation HowTo A tinkerer genius discusses energy conservation and his ladder system for accessing the attic (where a lot of energy-saving work happens).
- PennFuture Energy Center Energy and energy efficiency news for the Commonwealth of Pennsylvania
- Phila area rife with building efficiency upgrade opportunities Philadelphia Inquirer article discusses recent study showing Philadelphia’s inner-ring suburbs stand to save from energy conservation retrofits.
- Philadelphia Row-house Manual A design, maintenance, and modifications manual for our most widely-used form of housing.
- Robert Monk Robert Monk’s personal blog
- SolarCities (DOE) Solar PV Levelized Cost Interactive Comparator Simple graph compares ‘levelized cost’ of energy from solar PV to conventional grid rates, with a time-slider interactive feature.
- The Circuit Detective – Solve Home Electrical Problems Yourself! Electrical troubleshooting procedures pitched to homeowners.
- The Energy Co-op Blog from a leading alternative energy provider in PECO territory, includes fun conservation tips.
- Weatherization: the anti-Solyndra Salon.com article praising the continued success of the federal Weatherization Assistance Program (WAP), low-income energy-savings and job-creation.
- West Philly Tool Library Official site of WPTL, Philly’s own community tool lending library: like a book library, but tools!
- WestPhillyLocal .com Site name say sit all.
- Bartram's Gardens Founded in Philadelphia’s colonial era, today the gardens continue pioneering in horticulture and agriculture with a variety of herbs, trees and other vegetation in an arboretum/gardens on the Schulkill River banks, and a new farm abutting sadly neglected
- HiddenCity Philadelphia Surprising places it takes an adventurer to discover; events, too.
- Philly Household Hazardous Waste Drop-off Schedule City of Philadelphia dates and places for disposing of spent batteries, CFL lamps, unused paint and cleaning products, etc. LovePhilly: don’t pour these in the drain or send them out with the trash.
- Reading Terminal Market Purveyors of fine foods and foodie stuff, all under one roof downtown under the PA Convention Center
- Secret Garden on the Rails Jacques-Jean Tiziou shows some dramatic natural and urban and naturalized-urban scenes along abandoned rails of Philadelphia
- Sketch Burger, Fishtown A vegan-friendly burger joint with a #1 in Philly contender beef burger, best fries that somehow stay fresh for 1/2 hour while you tackle burger, and a vegan cafe vibe of friendly folks.
- WXPN: Philly sings in key of love Love songs by Philly artists