Tri-rated cable is the standard wire for control panels and switchgear in the UK, and one of the most common questions we are asked is what the “tri” actually means. Here is a plain-English guide to tri-rated cable, its ratings and where it should be used.
What is tri-rated cable?
Tri-rated cable is a single-core, flexible, PVC-insulated wire approved to three different national standards at once. One cable meets the British, American and Canadian requirements, so a panel builder can stock one product instead of three. It is also known as BS 6231 cable, panel wire or switchgear wire.
The three ratings are:
- BS 6231 Type CK from the British Standards Institution
- UL appliance wiring material (Subject 758), recognised as AWM Styles 1015, 1028, 1283 or 1284 depending on size
- CSA C22.2 No. 127, Type TEW from the Canadian Standards Association
How is tri-rated cable made?
A tri-rated cable has a Class 5 flexible plain copper conductor to BS EN 60228, covered with heat-resisting, flame-retardant PVC insulation. There is no outer sheath. The fine stranding makes it easy to route and terminate inside a crowded enclosure, and it is available in a full range of colours so circuits can be identified at a glance.
Tri-rated cable voltage and temperature ratings
Because each standard tests differently, the ratings vary slightly depending on which approval you are working to:
- Voltage: 600/1000 V under BS 6231, and 600 V under UL and CSA
- Temperature: up to 105°C conductor temperature under UL and CSA. BS 6231 sets 90°C for continuous use, with higher temperatures allowed for limited periods
- Flame performance: flame retardant, tested to BS EN 60332-1-2, UL VW-1 and CSA FT1
- Bending radius: typically six times the overall diameter
When equipment has to pass a UL or CSA inspection, the inspector will look for the UL style number and CSA marking printed on the insulation, so check the marking matches what your specification asks for. Our UL and CSA cable sourcing FAQs cover how these approvals work in more detail.
What is the current rating of tri-rated cable?
There is no single current rating for tri-rated cable. It depends on the conductor size, the ambient temperature inside the panel, how many cables are bunched together and how they are installed. A cable in free air will carry more than the same cable packed into trunking with dozens of others in a warm enclosure.
Always take the figure from the manufacturer’s data sheet for the exact size and apply the derating factors for your installation. If you are designing to BS 7671 or a North American panel standard, use the method that standard sets out. If you are unsure which size you need, our team can advise.
Where is tri-rated cable used?
Tri-rated cable is designed for internal wiring of equipment, including:
- Control panels and switchgear
- Motor control centres and motor starters
- Relay and instrumentation panels
- Machine control cabinets built by OEMs
It is not intended as fixed building wiring. For North American building wire, look at types such as TFFN or THHN instead.
Frequently asked questions about tri-rated cable
Why is it called tri-rated cable?
Because it carries three approvals at once: BS 6231 in the UK, UL in the USA and CSA in Canada.
Is tri-rated cable the same as BS 6231 cable?
Tri-rated cable is manufactured to BS 6231 Type CK, so all tri-rated cable is BS 6231 cable. Not every BS 6231 cable carries the UL and CSA approvals, though, so check the marking if you need all three.
Is tri-rated cable suitable for UL or CSA equipment?
Yes, that is its main advantage. The UL AWM style and CSA TEW approvals mean it can be used for internal wiring of equipment that needs to meet UL or CSA requirements, as well as UK and European panels.
Is tri-rated cable flame retardant?
Yes. The PVC insulation is flame retardant and tested to BS EN 60332-1-2, VW-1 and FT1. It is not a low smoke zero halogen (LSZH) cable, so check your specification if LSZH is required.
Where can I buy tri-rated cable in the UK?
Quadrant Cables supplies UL and CSA certified tri-rated cable from our Manchester distribution centre, with fast delivery across the UK and Europe.
Speak to the Quadrant Cables team
Need UL or CSA-approved cables, fast? Tell us the sizes, colours and quantities you need and we will confirm stock and send a quote. Call us on +44 (0)161 879 9898 or contact us online.
Quadrant Cable Services Ltd, Unit 2 Crown Business Centre, George Street, Failsworth, Manchester M35 9BW.
