This is not a checklist post. We covered the gauge tables and the GFCI rules a year ago in the 2026 holiday-lighting post and they have not changed. What did happen in 2027 is the season itself. From the second week of November through the third week of December, we ran five service calls that each started with "the lights stopped working" and ended somewhere very different. Five addresses, five failure modes, five things the homeowner did not see coming. The rest of the post is the service-call diary.
Call 1 - Dundas, November 18: the extension cord that melted into the railing
A homeowner off Governors Road called Tuesday morning. The icicle lights on her back deck had cut out overnight. By the time we arrived she had already pulled the cord and found a section of jacket about 25 cm long that had softened and re-hardened into a flat strip welded to the cedar deck railing. The cord was a 16-gauge indoor SJT extension - the standard orange one from the home center - feeding two strings of warm-white LEDs through a daisy-chained second cord.
What we measured: about 9.2 amps continuous on a 16-gauge cord rated for 13 amps intermittent. The cord was within rating. The problem was geometry. Where the cord crossed the cedar railing, the homeowner had snugged it tight with a black UV-resistant cable tie. The tie compressed the jacket against the railing, the jacket lost its ability to shed heat, surface temperature climbed into the 70°C range over a 12-hour overnight run, and the jacket softened. By morning it was a foam-textured strip stuck to the wood.
The fix: replace the cord with a 14-gauge SJTW outdoor run, route it loose with cable clips rated for the temperature, no compression at any contact point. We also added a second outdoor receptacle near the far end of the deck to eliminate the daisy chain. About a 90-minute visit.
What we told her: the cord did not fail. The install did. The cord was the messenger.
Call 2 - Burlington, December 1: the GFCI that nuisance-tripped every time the temperature dropped
A 1980s house off New Street with a single outdoor GFCI feeding the entire front-yard display. Five strings of LED net lights, two inflatables, a projector. The GFCI held all day. At about 4:30 PM, as the temperature dropped from 2°C to -4°C, the GFCI tripped. The homeowner reset it. It tripped again within an hour. He swapped the receptacle for a new one from the hardware store on Saturday afternoon. New device, same pattern. He called us Sunday.
What we found: nothing wrong. The GFCI was doing exactly what a GFCI does. Cold-weather LED drivers leak a small amount of current to ground - typically 0.3 to 0.7 mA per string. As the temperature drops, leakage rises. With five strings plus the projector plus a damp connector at one inflatable inlet, cumulative leakage was tipping just past 5 mA on cold evenings, and the GFCI saw it.
The fix: split the load across two GFCIs on two separate branch circuits. We added a second outdoor receptacle on a new branch from the panel, moved half the display to it, and replaced the wet connector with a UL-listed twist-lock weatherproof connector on the inflatable inlet. The trips stopped.
What we told him: this is not a failure. The device is telling you the load profile and the wet connection are too much for one GFCI to swallow. He thought he had a bad part. He had a design problem.
Call 3 - Ancaster, December 7: the timer relay welded itself closed
A property off Wilson Street, full front-yard display, programmed on a heavy-duty outdoor mechanical timer rated 15 amps. The homeowner noticed the lights had been on all morning when they were supposed to shut off at 1 AM. She turned the dial manually. Lights stayed on. She unplugged the timer. Lights stayed on. The timer was no longer the switch in the circuit. It was just a hot piece of plastic.
What happened: load on the timer was about 11 amps continuous - five inflatables, two LED runs, a projector. Within nameplate but at the edge of what a light-duty mechanical timer's contacts handle for continuous duty. Over six weeks the contacts arced slightly on every off-cycle. By early December the contact surfaces had welded. The relay was permanently closed. The off-position on the dial mechanically moved the cam, but the welded contacts kept conducting.
The fix: a hardwired contactor-based outdoor timer in a NEMA 3R enclosure, switched by a 24 VAC pilot from an indoor astronomical timer. The contactor handles the load; the timer handles the control. Same logic as a commercial parking-lot lighting circuit, sized for residential. Three-hour install including the new enclosure and a low-voltage control run inside.
What we told her: the timer was not the right product for the load. It worked for one season because the contacts were fresh. Year two was always going to end this way.
Call 4 - Stoney Creek, December 12: the dimmer that smoked at midnight
A house off Lake Avenue. The homeowner had installed indoor warm-white string lights along the staircase, controlled by a wall-mounted dimmer he had picked up at a big box. Around midnight on a Saturday his wife smelled hot plastic at the staircase. By the time he got there the dimmer face was warm enough to feel through the cover plate. He killed the breaker.
What we found: a Lutron Diva incandescent-rated dimmer controlling a 4.2-amp string of older incandescent C9 bulbs and one segment of LED that he had spliced in to "save energy." The dimmer was rated 600 watts incandescent - plenty for the 500-watt total load. The fault: the LED segment had failed shorted across one driver, the dimmer's triac was now switching a partially-shorted load, and heat dissipation in the dimmer body had nowhere to go because the gang box was a standard plastic non-heat-rated enclosure stuffed with extra wire.
The fix: replace the dimmer with a Lutron Caseta LED-rated unit, remove the spliced LED segment, re-terminate the staircase string on its own switched leg with a proper splice cover, and replace the plastic gang box with a metal box that dissipates heat. Two-hour visit.
What we told him: dimmers fail in two ways. The load they were designed for changes, or the box around them stops doing its job. Both happened at once.
Call 5 - Hamilton, December 19: the lights that flickered, then dimmed, then half went dark
A century home on the mountain. The homeowner had eave-mounted permanent LED holiday lights installed three years ago by a competitor we know does competent work. On a cold Wednesday evening the front-of-house segment started flickering. By the time the homeowner pulled out his phone to call, half the front had gone dark and the half still working was visibly dimmer than the side and back.
What we found: an open neutral. The eave-light circuit was sharing a multi-wire branch circuit (two hots, one shared neutral) with an interior bedroom circuit. The shared neutral connection at a junction box in the attic had loosened over three winters of thermal cycling. When the neutral opened, the two hot legs were now in series across the loads. Voltage split unevenly. The eave lights dimmed; the bedroom side overvolted and had already blown two LED bulbs.
The fix: re-terminate the neutral at the attic junction box with a torqued wire connector, re-energize, verify at the panel that the neutral carries the expected current. We added a label to the junction box noting that it serves a shared neutral, so the next person up there knows what they are looking at.
What we told him: this is the same fault we look for after an ice storm, not specific to holiday lighting. The lights were the visible symptom this time. The fix is the same one we describe in the ice-storm aftermath post when a homeowner reports flickering after the power comes back.
What was on the panel at every one of these calls
One Stab-Lok. Three Siemens or Eaton panels installed since 2005. One Federal Pioneer from the 1970s that has been on our "really should replace this" list through two prior visits. None of the failures this season had to do with the panel itself. The failures were all in the circuit downstream - the cord, the timer, the dimmer, the splice, the neutral. The panel is the part that usually holds up. The accessories are the part that fail.
For the gauge-and-GFCI fundamentals - the table, the in-use cover rules, the timer load math - the prior season's post still applies. The 2026 holiday lighting post is where we wrote those down. This year's post is what we found when those fundamentals were not followed.
When to call us
If something on your display has changed - a dimmer that runs warm, a GFCI that has started tripping in cold weather, a timer that does not click off, a string that has gone half-dark - we have visits open through the end of the year. Book a visit across Hamilton, Burlington, Waterdown, Ancaster, Dundas, Stoney Creek, Oakville, and the Muskoka cluster.