2025.11.12 – Grounding with C-taps: clear markings, the right die, and a clean, centred crimp

Key Takeaways

What the markings mean. The stamps “35–40” and “10–25 CU” identify the run and tap size ranges in square millimetres for a copper connector; this combination matches Cembre’s C35-C35 family rather than C35-C16.
Why the die matters. Die codes MC35, MC35-50, and MC35-C map directly to tool force classes: around 50 kN for MC35/MC35-50 and 130 kN C-head tools for MC35-C. The die choice sets both fit and crimp count.
How to position. A C-tap has a single open throat; place run and tap side-by-side in that throat and make the oval indentation at the body’s centre. Two symmetric crimps are used with ~50 kN tools; one centred crimp is used with 130 kN heads.
Sealing the job. For wet or buried work, wraparound heat-shrink sleeves with hot-melt adhesive seal the connection without cutting a continuous run.

Story & Details

Naming the part. The component is a copper C-tap (also called a C-clamp): a compression connector used to take a branch from a continuous grounding conductor or to make an overlapped joint. The official instructions label the series “for tap and joint connections” and present the installation sequence with figures.

Reading the body. On the photographed piece, “35–40” denotes the run range and “10–25 CU” denotes the tap range for copper conductors. Cembre’s documentation pairs those ranges with the C35-C35 model. The same material specifies an oval crimp geometry.

Die–tool pairing. The matrix (die) is the matched jaw set that forms the correct oval profile. For the C35 family, manufacturer tables assign MC35 to HT45-class tools, MC35-50 to HT51/B500-class tools, and MC35-C to 130 kN C-head tools such as HT120/HT131. Those tables also state how many impressions are required for each size.

Crimp count and placement. Practice aligns with tool class: ~50 kN handheld or battery tools require two impressions, placed symmetrically about the connector’s centre; 130 kN heads specify one centred impression. In all cases, run and tap sit side-by-side within the single C throat and the indentation is centred on the body—not on the lips—so the arc collapses and forces both conductors against the back of the C.

Finishing for the environment. Identification tape handles basic marking. Where moisture or burial is expected, use wraparound sleeves with rail-and-channel closure and hot-melt adhesive. These sleeves are designed for repair and re-jacketing without cutting an in-service run and are documented by both 3M (HDCW) and TE Connectivity (Raychem CRSM).

Conclusions

What it is and how to finish it. A connector stamped “35–40” and “10–25 CU” is a Cembre C35-C35 copper C-tap. Seat run and tap together in the single throat and crimp at the middle—two centred, symmetric impressions with ~50 kN tools using MC35/MC35-50, or one centred impression with a 130 kN C-head using MC35-C. For harsh exposure, seal with a wraparound heat-shrink sleeve with adhesive for a durable, moisture-resistant finish.

Sources

Cembre — “C” type connectors: instruction sheet with Figures 1–3 and die selector chart (PDF):
https://cdn.cembre.com/prodotti/documenti/05I016IEAR%7Bconn.%20C_05I016IEAR_6260120%7D_PIN_multi3.pdf

3M — HDCW wraparound heat-shrink cable repair sleeves (PDF datasheet):
https://multimedia.3m.com/mws/media/103267O/3m-hdcw-wraparound-heat-shrink-cable-repair-sleeves.pdf

TE Connectivity — Raychem CRSM wraparound heat-shrink sleeves (PDF datasheet):
https://www.te.com/content/dam/te-com/custom/documents/windsolutionguide/energy-crsm-datasheet-10-18-epp3192-ieee.pdf

YouTube (institutional; single verified video relevant to heat-shrink installation):
https://www.youtube.com/watch?v=41UH7LftkDM

Appendix

C-tap / C-clamp. A copper, C-shaped compression connector that bonds a branch conductor (tap) to a continuous main conductor (run) or forms an overlapped joint; crimped with an oval profile.

Cembre. Manufacturer of compression connectors and hydraulic crimping systems; its instruction sheet defines markings, die references, and crimp counts for C-taps.

Copper (CU). Material designation stamped on the connector indicating suitability for copper conductors; supplied as bright (bare) or tin-plated finishes.

Die (matrix). The matched jaw set installed in the crimping tool; for this size family the codes are MC35, MC35-50, or MC35-C, each tied to a compatible tool force class.

Mastic (EPR self-fusing tape). An elastomeric, self-amalgamating layer often used beneath an outer PVC wrap to seal and cushion a joint against moisture.

Oval crimp. The centred indentation geometry specified for these connectors; it collapses the arc of the C and bears both conductors against the back of the connector.

Run. The uncut main conductor continuing past the connection point; the C-tap clamps onto it without severing it.

Tap. The branch conductor added to the run via the C-tap; its permissible size range is stamped separately on the body.

Tin-plated (ST). A corrosion-resistant finish offered alongside bright copper on the same connector series.

Tool force classes. Families around 50 kN use MC35/MC35-50 and require two impressions; 130 kN C-head families use MC35-C and require one centred impression.

Wraparound heat-shrink sleeve. A field-installed sleeve that wraps around an in-service cable and closes with a rail-and-channel; heating shrinks the sleeve and activates hot-melt adhesive to seal the joint.