Temperature Busbar DC side

Been meaning to post about this for a while actually.

Swapped out my chunky 95mm² DC cables for copper busbar last month — 4mm thick, 30mm wide — running between my Fogstar batteries and the Victron MultiPlus. Cleaner install, less voltage drop, all good in theory.

What I didn't anticipate was how much heat builds up on the busbar itself, particularly around the DC isolator connections. I've got a 250A rated isolator in the circuit and even at moderate loads (say, 80-100A) the busbar around that isolator gets noticeably warm. Not burn-your-fingers hot, but enough to make me dig out a cheap IR thermometer.

Sitting around 38-42°C ambient on a mild day. Is that a concern or just physics doing its thing?

A few things I'm wondering:

• Does anyone actually monitor busbar temps continuously, or just do spot checks?
• Is the heat concentrating at the isolator because of contact resistance there specifically?
• Would wider/thicker bar make a meaningful difference, or is the isolator itself the bottleneck?

My gut says the isolator contacts might not be torqued quite right, or possibly it's just slightly undersized for my peak loads (which can spike to 180A when the inverter works hard). Planning to retorque everything and recheck.

Curious whether others have seen similar on copper bar installations — especially anyone running Victron kit with a busbar DC side rather than traditional cabling. There's not loads written about this for smaller UK off-grid setups specifically.

@Nessa73 good move going to busbar — the current density on 4×30mm copper is substantially better than 95mm² flex.

Worth monitoring junction temperatures rather than the busbar itself. The busbar copper will barely warm up under normal loads, but bolted connections are where heat concentrates if torque is insufficient or surfaces weren't prepared properly.

I'd recommend:

• Clean contact faces with isopropyl before assembly
• Use belleville/spring washers rather than plain
• Torque to spec and re-check after first few thermal cycles

On my cabin build I use a cheap IR thermometer periodically across all connections — anything more than 5-10°C above ambient at a joint warrants investigation. Victron's own documentation suggests keeping DC connections below 60°C continuous.

What terminal arrangement did you use at the Victron end — direct bolt to the inverter lugs?

@Nessa73 worth keeping an eye on that busbar temperature under load — I've got a similar setup on my static caravan with Victron kit and initially underestimated heat buildup at the connections rather than the busbar itself.

Biggest culprit for me was slightly undertorqued bolts at the battery terminals. Looked fine visually but the connection resistance was enough to cause noticeable warmth. A proper torque wrench and some Vaseline on the copper made a real difference.

If you haven't already, an IR thermometer is dead cheap and lets you spot-check everything under EV charging loads when current is actually high. That's when any weak points really show themselves.

Ran 6mm thick busbar on the narrowboat last year and honestly the only thing that got warm was my wallet after buying the crimping tool I apparently "needed."

@Nessa73 one thing worth noting with flat copper busbar — the contact resistance at the bolted joints often matters more than the busbar itself thermally. A 30×4mm run can be carrying 100A+ without significant self-heating, but a poorly torqued M8 bolt on a tinned lug will glow eventually.

When I installed busbar between my Fogstar Drift cells and the Victron Multiplus, I used a calibrated torque wrench (typically 10-12Nm for M8 on copper) and applied a thin coat of NO-OX-ID or similar anti-oxidant compound on every mating face. Worth checking with an IR thermometer under realistic load — any joint running more than ~10°C above ambient is worth investigating before it becomes a proper problem.

The busbar itself should barely register if sized correctly.