Key takeaways
- The drawing defines the shape; the RFQ has to define the duty, the environment and the volume.
- State the current, the ambient, the allowable temperature rise and the fault level so the section can be checked.
- Name the finish, the thickness and the mating surfaces, including any masked areas.
- Say what the quote should break out, so two suppliers can be compared line by line.
Why busbar RFQs stall
A busbar RFQ usually stalls for one of three reasons. The drawing is missing a tolerance that changes the process. The electrical duty is implied rather than stated, so the supplier cannot check the section. Or the volume and delivery pattern are left open, so the supplier prices a range and the buyer cannot tell what was assumed.
The result is a set of quotes that cannot be compared. One supplier prices a bar from the drawing exactly as drawn. Another adds material because the current looks high for the section. A third quotes a lower grade because the environment was not described. The totals differ, but the differences are in the assumptions, not the efficiency.
A useful busbar RFQ is a short document with four blocks: the drawing, the electrical duty, the environment and finish, and the commercial frame. Each block answers a question the supplier would otherwise have to guess.
The drawing block
Send the current revision as a PDF, and the native CAD file if you have one. State the revision in the email as well as on the drawing, because drawings get separated from messages. If the part is still in design, send the concept and mark which features are fixed and which are open.
The drawing needs a title block with material, temper, general tolerance, finish and a mass or a note that the mass is to be confirmed. It needs datums for the hole pattern and the bend positions. If a bend is dimensioned to an intersection rather than to a tangent, say so, because two suppliers will interpret it differently.
Add the edge and burr condition. A busbar with a sharp punched edge is normal for some assemblies and unacceptable for others, particularly where a cable or a hand will touch it. A note such as deburr all edges, burr height not to exceed a stated value, removes the question.
A PDF without a revision is a drawing without an owner
Name the file with the part number and revision, and repeat both in the RFQ. It takes a few seconds and prevents a quote against a superseded bend layout.
The electrical duty
Give the working current, the system voltage, the ambient temperature inside the enclosure and the allowable temperature rise. If the bar is part of an assembly tested to a standard, say which standard and which clause applies. The supplier can then check that the section is plausible rather than guessing from the outline.
Add the fault level. A busbar that carries its rated current continuously still has to survive a short circuit for the clearing time. State the prospective fault current and the duration, or the withstand rating the assembly must meet. A supplier who is not told will price a bar that is adequate for the load and not for the fault.
State the voltage drop limit if the design has one. A long run at low voltage can fail a drop limit before it fails a temperature limit, and the fix may be a larger section or a different joint. Give the length of the run and the acceptable drop.
The environment and the finish
Describe where the bar will live. Indoor, inside a sealed enclosure, is different from a humid plant room, a coastal site or an outdoor cabinet. Temperature range, condensation, salt and chemical exposure all affect the plating choice and the cost.
Name the finish and the thickness. Tin, silver, nickel and bare copper are not interchangeable. Tin is the common choice for general joints, silver for high current and repeated mating, nickel for wear and some high-temperature duties. Give the standard, the minimum thickness and the areas that must be coated.
Say which surfaces must be masked. A powder-coated bar needs bare contact areas at the joints, and the masking boundary affects both the coating cost and the inspection. If the whole bar is coated, the joint faces need a defined treatment.
Interfaces and joints
A busbar is rarely a stand-alone part. It bolts to a terminal, a breaker, another bar or a cable lug. Send the mating hardware and the hole pattern, including the bolt size, the washer type and the torque the assembly will use. If the joint is bolted to a plated terminal, state the mating finish so the supplier can consider galvanic compatibility.
Say whether the joint is bolted, clamped or welded. A welded joint changes the material condition near the weld and may need a different temper or a post-weld treatment. A bolted joint needs flatness, hole position and a surface that will not relax under load.
If the bar is part of a stack, give the stack order and the total thickness. A bar that is dimensioned on its own may not fit once washers and a second bar are added. The same applies to clearance to the enclosure and to other phases.
The commercial frame
Give the annual volume, the release size and the delivery pattern. A supplier pricing 500 pieces a year against a single release will quote differently from one pricing 500 pieces a month. State the expected programme life and whether the volume is firm or forecast.
State the Incoterm and the delivery destination. FOB and DDP quotes are not comparable, and a quote delivered to a port is not the same as one delivered to a warehouse. Add the packaging requirement if the bars are long, polished or plated, because packing is a real cost line.
Ask for the quote to be broken into metal, conversion, plating, packing and freight, with the copper reference and the date it was taken. That breakdown lets you compare suppliers on the same basis and shows which line to discuss when a price looks high.
Say what documentation you need with the shipment: material certificate, plating certificate, dimensional report, first article, declaration of conformity. A supplier who knows the paperwork requirement at RFQ stage can price it. One who learns at dispatch will either add a charge or send an incomplete pack.
| Input | What to send | What it changes |
|---|---|---|
| Drawing revision | PDF and native CAD, revision stated | Shape, bend layout and tooling |
| Material and temper | Grade, temper and conductivity basis | Metal cost and formability |
| Working current | RMS current and duty cycle | Section and temperature rise |
| Fault level | Prospective current and duration | Short-circuit withstand |
| Ambient | Enclosure temperature and range | Derating and finish choice |
| Finish | Type, standard, thickness, masked areas | Plating cost and joint resistance |
| Joints | Mating parts, hardware and torque | Flatness, hole pattern and plating |
| Volume | Annual, release size and pattern | Process route and setup amortisation |
| Documentation | Certificates, FAI, reports | Inspection cost and lead time |
Every row is a question the supplier would otherwise answer with an assumption. State the assumption only when you are willing to accept it.
The send-ready checklist
Before the RFQ goes out, read it as a supplier would. Can you calculate the mass? Can you see which features are critical? Can you tell whether the bar will be plated on a rack or in a barrel? Can you price the packing? If any answer is no, the quote will contain a guess.
Keep the RFQ short enough to be read. A one-page cover note with the drawing attached is usually better than a long document that repeats the drawing. Put the open questions at the end and give a date for answers, so the supplier knows what to ask before the quote is due.
When the quotes come back, compare the breakdowns before the totals. A low total built on a thin plating or a lower grade is not a saving. A high total with a clear metal reference and a stated yield may be the more honest number.
- Drawing at the current revision, with datums and general tolerance
- Material grade, temper and conductivity requirement
- Working current, ambient, allowable rise and voltage drop limit
- Fault current and duration, or the assembly withstand rating
- Finish type, standard, thickness and masked areas
- Mating parts, hardware, stack order and torque
- Annual volume, release size, delivery pattern and Incoterm
- Documentation and inspection level required with each shipment
Frequently asked questions
What is the minimum information for a busbar quote?
A dimensioned drawing, the material and temper, the working current, the ambient temperature, the finish and the annual volume. Without those six, a supplier can only price a shape. The fault level, joint details and documentation add accuracy but are sometimes supplied after a first indicative quote.
Should I send a 3D model with a busbar RFQ?
Yes, if one exists. A native model or a STEP file helps the supplier check the flat pattern, the bend clearance and the mass. The drawing still governs, so state that the model is for reference and that the drawing revision controls in any conflict.
How do I compare busbar quotes with different copper references?
Ask each supplier for the copper reference, the date it was taken and the metal content in kilograms, then rebuild each quote at one common reference. Compare the conversion and plating lines separately. A total that mixes different copper dates is not a like-for-like comparison.
Do I need to specify the plating thickness?
Yes. Plating thickness affects corrosion resistance, contact resistance and cost. Give the standard and the minimum thickness, and say which areas must be coated or masked. A finish named without a thickness will be priced at whatever the supplier assumes.
Sources and further reading
- IEC 61439-1, Low-voltage switchgear and controlgear assemblies, general rules
- Qumek busbar RFQ and drawing review templates
- Copper Development Association, copper for busbars
Qumek Engineering Desk
Engineering team
The engineering team behind Qumek drawings, DFM notes, tolerances and inspection standards. Every guide is reviewed against the drawings and processes used on live programmes.
Send a busbar RFQ that gets comparable quotes
Use the drawing, duty and volume blocks above, then send the pack to the engineering desk for a review before it goes to suppliers.
Send a drawing