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Cryogenic wire specifications

Material properties		Phosphor bronze	Copper	Nichrome	Manganin
Melting range		1223 K to 1323 K	1356 K	1673 K	1293 K
Coefficient of thermal expansion		1.78 × 10^-5	20 × 10^-6	—	19 × 10^-6
Chemical composition (nominal)		94.8 % copper, 5% tin, 0.2% phosphorus	—	80% nickel, 20% chromium	83% copper, 13% manganese, 4% nickel
Electrical resistivity (at 293 K)		11 µΩ•cm	1.7 µΩ•cm	120 µΩ•cm	48 µΩ•cm
Thermal conductivity (W/(m•K))	*0.1 K*	NA	9	NA	0.006
	*0.4 K*	NA	30	NA	0.02
	*1 K*	0.22	70	NA	0.06
	*4 K*	1.6	300	0.25	0.5
	*10 K*	4.6	700	0.7	2
	*20 K*	10	1100	2.6	3.3
	*80 K*	25	600	8	13
	*150 K*	34	410	9.5	16
	*300 K*	48	400	12	22

	AWG	Resistance (Ω/m)			Diameter (mm)	Fuse current air (A)	Fuse current vacuum (A)	Number of leads	Name	Insulated diameter (mm)	Insulation type	Insulation thermal rating (K)	Insulation breakdown voltage (VDC)
	AWG	4.2 K	77 K	305 K	Diameter (mm)	Fuse current air (A)	Fuse current vacuum (A)	Number of leads	Name	Insulated diameter (mm)	Insulation type	Insulation thermal rating (K)	Insulation breakdown voltage (VDC)
Phosphor bronze	32	3.34	3.45	4.02	0.203	4.2	3.1	1	SL-32	0.241	Polyimide	500	400
								2	DT-32	0.241	Polyimide
								4	QT-32	0.241	Polyimide
								4	QL-32	0.241	Polyimide
	36	8.56	8.83	10.3	0.127	2.6	1.4	1	SL-36	0.152	Formvar^®	378	250
								2	DT-36	0.152	Polyimide	500	400
								4	QT-36	0.152	Formvar^®	378	250
								4	QL-36	0.152	Polyimide	500	400
Nichrome	32	33.2	33.4	34	0.203	2.5	1.8	1	NC-32	0.241	Polyimide	500	400
Copper	30	0.003	0.04	0.32	0.254	10.2	8.8	1	HD-30	0.635	Teflon^®	473	250
Copper	34	0.0076	0.101	0.81	0.160	5.1	4.4	2	CT-34	0.254	Teflon^®	473	100
Manganin	30	8.64	9.13	9.69	0.254	4.6	4.3	1	MW-30	0.295	Formvar^®	378	400
	32	13.5	14.3	15.1	0.203	3.8	3.5	1	MW-32	0.241	Formvar^®		400
	36	34.6	36.5	38.8	0.127	2.6	2.5	1	MW-36	0.152	Formvar^®		250

Phosphor bronze wire

Phosphor bronze wires (Quad-Lead™, Quad-Twist™, Duo-Twist™, and nonmagnetic) are suitable for almost all cryogenic applications. The low magnetoresistance of these wires makes them the ideal choice for magnetic field use.

Physical Properties

Melting range: 1,223 K to 1,323 K (950 °C to 1050 °C)

Coefficient of thermal expansion: 1.78 × 10^-5

Thermal conductivity: 48 W/(m • K) at 293 K

Electrical resistivity (annealed): 1.15 × 10^-7 Ω • m at 293 K

Specific heat: 376.4 J/(kg • K)

Stress relief temperature (1 h): 423 K to 498 K (150 °C to 225 °C)

Chemical composition: nominal 94.8% copper, 5% tin, 0.2% phosphorus

Wire insulation

Polyimide

Polyimide insulation is by far the most versatile insulation option available for cryogenic wiring. It will operate at temperatures in excess of 493 K (220 °C) for intermittent duty and has exceptional resistance to chemical solvents and burnout. Polyimide exhibits excellent resistance to radiation exposure and, as such, is used extensively in spaceflight and high-energy physics applications. Polyimide can be removed mechanically during terminal preparation and is rated to 3525 VAC for 32 AWG and 2525 VAC for 36 AWG.

Polyvinyl Formal (Formvar^®)

Formvar^® has excellent mechanical properties such as abrasion resistance and flexibility. The film will stand excessive elongation at low temperature without rupture, making it a great choice for wiring applications with tight bend radii at ultra-low temperatures. However, care is advised, as Formvar® has a tendency to craze upon contact with solvents such as toluol, naphtha, and xylol; therefore, it should be given an annealing preheat prior to varnish application. Formvar® can be removed mechanically during terminal preparation and is rated to 3525 VAC for 32 AWG and 2525 VAC for 36 AWG.

Note: At Lake Shore, we strip both Polyimide and Formvar^® mechanically using an Eraser Rush Model RT-2 mechanical stripper.