Subdivision (

a) of

Section shall not apply to a loan made by a trust described in

Section 401(

a) of the Internal Revenue Code to the employer (or to a renewal of such a loan or, if the loan is repayable upon demand, to a continuation of such a loan) if the loan bears a reasonable rate of interest, and if (in the case of a making or renewal)— (

a) The employer is prohibited (at the time of the making or renewal) by any law of the United States or regulation thereunder from directly or indirectly pledging, as security for such a loan, a particular class or classes of his assets the value of which (at that time) represents more than one-half of the value of all his or her assets; (

b) The making or renewal, as the case may be, is approved in writing as an investment that is consistent with the exempt purposes of the trust by a trustee who is independent of the employer, and no other similar trustee had previously refused to give that written approval; and (

c) Immediately following the making or renewal, as the case may be, the aggregate amount loaned by the trust to the employer, without the receipt of adequate security, does not exceed percent of the value of all the assets of the trust. (

d) For purposes of subdivision (b), the term “trustee” means, with respect to any trust for which there is more than one trustee who is independent of the employer, a majority of those independent trustees. For purposes of subdivision (c), the determination as to whether any amount loaned by the trust to the employer is loaned without the receipt of adequate security shall be made without regard to

Section 17639.