• Introduction and low thermal challenges
• TBP5 50A low-thermal binding post
• TBP4 lower cost 5-way low-thermal binding post
• TBP3 30A low-thermal binding post
• Banana jacks and plugs
  • TBU1-0-1-001 4 mm Banana Plug
• Nuts and washers
• Fork spade lugs
• Closed spade lugs
• Summary and conclusion

Introduction to low thermal interconnect challenges

Sensitive electrical signals are not easy to measure and interface. Small parasitics due to imperfect connection for voltage measurements start to contribute into significant errors if application require measurements or sourcing of the small level signals some millivolts DC. Specialized instruments designed to work with these levels often utilize specialized shielded connectors with special materials, crimped or welded junctions and unplated copper surfaces. One of common everyday applications that pay attention to such details are thermocouple temperature sensors and interfaces, where Seebeck coefficient is utilized to determine temperature of the tip by measuring small generated voltage differential.

But often goal is to transmit small level signals across some distance and across different temperatures, so opposite of this thermocouple effect is required. This can be achieved by using unplated copper-only interconnects along whole signal path from source to destination. No plating is important for the lowest possible parasitic thermal EMF. Dissimilar metals, in contact with each other with thermal gradient present produce a small offset voltage. This voltage value depends on junction temperature and is therefore called a thermal EMF. The rate of change of this thermal EMF voltage with temperature is a function of the metals used in combination. The sense of the voltage produced is either positive or negative, depending on which side of the combination is being considered the input. Most, if not all electronic components, even simple resistors, capacitors, diodes have internal intermetallic combinations, and eventually connected to PCB/wire copper conductors as a final junction. Hence, copper is the typical reference metal in thermal EMF figures and analysis. Here are some examples of typical thermoelectric coefficients (also known as Seebeck coefficients) of bi-metal connections with copper.

Material	Thermoelectric Potential (EMF)	Error magnitude on 1VDC with 5°C ΔT
Copper-Copper	< 0.2 µV/°C	<1 ppm
Copper-Silver	-0.3..+0.03 µV/°C	-1 ppm
Copper-Gold	+0.01..+0.2 µV/°C	+1 ppm
Copper-Cadmium/Tin	0.3 µV/°C	1.5 ppm
Copper-Lead/Tin	1…3 µV/°C	15 ppm
Copper-Zeranin	-1.3 µV/°C	-6.5 ppm
Copper-Brass	-1.6 µV/°C	-6.5 ppm
Copper-Evanohm	+2.0 µV/°C	+10 ppm
Copper-Manganin	-1.7..-3.0 µV/°C	-15 ppm
Copper-Aluminum	-4.0 µV/°C	-20 ppm
Copper-Nickel	-10..-22.0 µV/°C	-55..-110 ppm
Copper-Constantan	+39.7 µV/°C	-195 ppm
Copper-Kovar	40 µV/°C	200 ppm (0.02%)
Copper-Cupron	-45.0 µV/°C	-225 ppm
Copper-Silicon	400 µV/°C	0.2%
Copper-Copper Oxide	1000 µV/°C	0.5%

Table 1: Typical thermal EMF figures with different metal junctions

To minimize thermal offsets use only fresh clean cut copper wires and spade lugs. Do NOT solder connections to avoid dissimilar metals on contact area. Soldered connection can make parasitic offsets 1-3µV/°C, which is significant source of error for precision measurements. Make sure surfaces of copper contacts shiny, as copper oxide have very large thermal EMF. If copper oxidized, use soft abrasive pad to clean connections and attach wire immediately. Proper copper-copper connection have typical offset of 0.2 µV/°C or less, while oxidized/tinned connection can be more than 1000 µV/°C.

This attention to metal junctions and care is important even for large signal measurements when best uncertainty is required. Connecting precise low-noise 10 V source to multimeter or device under test during adjustment or calibration must be done with low thermal EMF terminals to preserve best stability and repeatability, since temperature is always changing a bit even in actively controlled laboratory environment. This is especially important for primary metrology work with 8½-digit instruments and quantum standards which are capable to deliver accurate voltages with stability better than 10^-9 but only when proper interconnects are used.

Connectors that fit the goal and provide such high quality connections are rather specialized and not available from normal electronics components shops such as Mouser, Digikey or Farnell. In fact even expensive commercial fancy connectors like this one are brass alloy and would generate large errors for microvolt signals. Other alternatives that are actually tellurium-copper with good performance like Pomona 3770 are expensive over 24 USD/piece, have nickel/gold plating and use very low quality brittle plastic. There were few other connectors from european manufacturers but they are even harder to get and often get obsolete just after few years. And there are always even more specialized copper connectors like LEMO FVN.1S.90x and EVP.1S.304 variants that are commonly used in Keithley 2182A and Keysight 34420A nanovoltmeters.

Most of these nice connectors are rather hard to get and this situation with lack of affordable copper connectors couldn’t last forever. Decade or so ago metalwork fab in China started to address this challenge since there is a noticeable demand for low thermal binding posts on the market. Eventually a set of copper hardware got manufactured in pilot volumes and now they are available under TESOO brand internationally. Ordering process is a bit manual, there is no website but folks on forums and in xDevs chat have a connection to TESOO representatives to order amounts of copper hardware with quantity from single units for various experiments use and to support hobby metrology projects. This article can be used as independed review of the items that TESOO has available, including old and experimental fabrication runs for special orders.

All hardware is available in single quantities but price discounts may apply for larger orders of same component, starting from 10 pcs qty and so on. If you have large order, ask TESOO for individualized pricing.

TBP5 50A low-thermal binding post – new in 2026

TBP5 binding posts are latest iteration of low-thermal high-quality copper terminals for metrology use. These posts are available for price around ~23-25 USD (August 2026) in single quantities. Each post is supplied with two copper M5 nuts, two copper washers, both LED-backlight and non-backlit sleeves and polycarbonate panel mount insulators. Top knob is fully removable, revealing full access to threaded rod for easy cleaning.

This design is based on older TBP3 design but with few updates (marked in bold):

• Same as predecessor TBP3 these posts support 5 ways of connection interface (sorted in connection quality preference):
  • Bare wire inserted into drilled side hole and crimped by knurled knob
  • Bare wire wrapped around the threaded rod and crimped by knurled knob
  • Spade lug terminated cable end
  • Banana jack inserted from the front
  • O-Ring terminal attached from the front (thanks to fully removable knob)
• Post body is made out of tellurium copper and has now extended length to better support multi-cable and high current connections
• Post body connection thread is now metric M5 to support larger O-ring terminals for higher current. Post is tested with currents up to 50 A DC.
• Available in both LED backlit and plain polycarbonate rings
• Available in unplated (best) and gold plated over nickel versions
• Available in grey or black plastic insulator color
• Available with number of colored knurl rings for easier identification

Comparison to TBP3 hardware (on the right) vs TBP5 (on the left):

This post easily supports multiple 50 amp copper lugs for heavy duty cable connections or mount on thick PCBA directly for best connection.

TBP4 lower cost 5-way low-thermal binding post

TBP4 is simpler and cheaper (half-price) variant of TBP3/TBP5 without ability to utilize LED ring backlight. It is using M4 rod body and smaller diameter D-hole for panel mount. It is NOT mechanically compatible with larger TBP3/TBP5 posts due to simpler construction of insulators. Order options and colors are same as top tier posts.

TBP3 30A low-thermal binding post

TBP3 posts were released around year 2024 and still going strong, available in various configurations and used in many projects globally. I’ve had dedicated page about them before. TBP3 are 5-way low thermal EMF binding posts with D tube and/or light pipe for LED backlight applications. These post were designed and built by volt-nut community enthusiasts to support various metrology projects and designs. Posts were designed and launched some years back but were under lengthy testing procedure for validation.

Approximate prices for small quantity are ~20 USD for pure copper version and about ~21 USD for gold-over-nickel plated copper version. Price drops down a little with larger quantity orders (10 pcs+).

Datasheet for TBP-3

Models and ordering information

Standard colors are black or gray bodies with black, white, red, blue, or green colored coded inserts. All binding post come with both D tube and light pipe.

Part-number for ordering follows the format : TBP3-A-B-XX. Designators and part list decode is available in table below:

Post model code	A designator, plating	B = insulation color	XX Insert color
TBP3-A-B-XX	0 = CuTe non-plated connector	0 = Black plastic color	00 – Black insert ring
	1 = CuTe + Nickel + Gold plated connector	1 = Milk grey plastic color	01 – White insert ring
			02 – Red insert ring
			03 – Blue insert ring
			04 – Green insert ring

Materials used in TBP3

Insulated thumb nut metal, molded in plastic : CuTe
Insulation material : PC = Polycarbonate
Mounting Base : Polycarbonate
Insulator holder : Polycarbonate
Lock washer : Cu
Hex Nut : M4 thread, Cu
Binding Post body : CuTe

The binding posts can be used with LED backlight. Therefore, three side LED’s are arranged in 120° angle to shine at the light pipe made out of frosted transparent polycarbonate.

Accessories

Additional accessories made of T2 copper, that are compatible with TBP-3 binding posts, are available on request.

Description	Part number
Low thermal e.m.f. fork terminal/spade lug	Spade lug 12-14 T2 Copper
Low thermal e.m.f. fork terminal/spade lug	Spade lug 22-16 T2 Copper
Low thermal e.m.f. ring terminal	O ring tongue 16-22 T2 Copper
Low thermal e.m.f. hex nut	#8-32 T2 Copper Hex Nuts

Photographs

I have also demo PCB module with RGB backlight for these TBP3 low thermal posts. It allows to set various colors for each individual post for appearance review and demonstration.

Features close-up photographs

Gold-over-nickel plated post version:

Pure-copper version for more critical low voltage metrology applications:

Here one of the posts with sanded surfaces to reveal nickel under gold surface as well as example side RGB-backlight placement on mounted PCB.

TBP2

TBP1 (now obsolete)

Special orders

PTFE insulated low leakage terminals (not available)

These special order posts were built for low leakage with PTFE rings as insulators. They are not keyed and bit tricky to use but provide very nice solution for high resistance builds.

They used fatter M4 nuts and copper washers from TBP3. Top fully copper knob was fully removable. Rod was supporting banana plugs but did not have side drill for bare wire crimping. I’ve reused these posts in recent Wavetek 4910 DC standard restoration.

Heavy mass copper nut (for grounding or nanovolt termination)

Banana jacks and plugs

TBU1-0-1-001 4 mm Banana Plug

Nuts and washers

Fork spade lugs

Closed spade lugs (O-ring terminals)

Summary and conclusion

I’ve used all of the above terminals for many different projects at xDevs in last decade or so and don’t have complains at this point. Price is not very low, but it’s far far better than alternative offerings from traditional suppliers or inadequate brass/steel posts.

Feel free to contact us for questions and comments. Discussion about this article and related stuff is also welcome at our own IRC-chat server: xdevs.com (port 4808, channel: #xDevs.com) if you like more real-time interaction with electronics engineering enthusiasts like the author of this article. There is also public xdevs forum where you can discuss many metrology questions with our small community.

Also if you are willing to order some copper hardware, participate in periodic group orders or contact to TESOO for individual ordering and pricing.

Projects like this are born from passion and a desire to share how things work. Education is the foundation of a healthy society - especially important in today's volatile world. xDevs began as a personal project notepad in Kherson, Ukraine back in 2008 and has grown with support of passionate readers just like you. There are no (and never will be) any ads, sponsors or shareholders behind xDevs.com, just a commitment to inspire and help learning. If you are in a position to help others like us, please consider supporting xDevs.com’s home-country Ukraine in its defense of freedom to speak, freedom to live in peace and freedom to choose their way. You can use official site to support Ukraine – United24 or Help99. Every cent counts.